That’s right, in this post I’m going to jot down all of the essential things you should know about that weird OE thing you keep hearing about, and why it’s so important for monarch conservation. If you are new to the world of monarchs, this will be like a crash course for you. And for the seasoned aficionados, keep this blog handy to pass out to anyone who needs it.

I’ll break this down into sections, the topics of which are based on the most common questions people have, starting with the main one, “what is OE?”

What is OE?

“OE” is an abbreviation for the species name of the parasite, which is Ophryocystis elektroscirrha. It is a microscopic protozoan (single-celled) organism that infects monarchs. It cannot be seen with the naked eye, only with a decent microscope, and then, only in adult monarchs. It cannot be detected in the caterpillar stage. I’ll paste a decent picture of the parasite, and where it can be found on monarchs, below.

The football-shaped things are the parasite, and at this stage, they are found mostly on the monarchs’ abdomen in a “spore” stage. A heavily infected monarch can have millions of these spores, and they are designed to slowly fall off the abdomen as the monarch flies around. Think of it like glitter. This is in fact how the parasite transmits itself. As the infected monarch is landing on, or even flying over, milkweeds, some of the parasites drop off and land on the milkweed leaves. Then, any monarch caterpillars on that milkweed will eat the spores, and then the infection cycle continues. The infection can ONLY transmit to a new host by consumption of the parasite spores.

What does OE do to the monarchs?

There are two parts to this section. First, I’ll describe what the parasite does to individual monarchs that are unfortunate enough to consume some spores as caterpillars. There is usually no noticeable effect on the caterpillar, and even in the pupal stage, it can be hard to see anything wrong. Sometimes, a pupa will show signs of dark spots, but these are only in serious infections. Lightly-infected pupae will look normal. The same is true for the adult monarch stage - a lightly-infected monarch will look completely normal. But a heavily-infected one will often have difficulty breaking free of its own pupal case, and fail to properly develop its wings, like the one pictured below. Those unfortunate monarchs will not live long.

If the infected monarch was able to successfully eclose and form its wings, it will then go on to live its life, flying around, mating, doing butterfly things, all the while dropping spores. This is in fact, what the parasite wants. Research has shown that these monarchs do have a slightly shortened life compared to uninfected monarchs (though it really depends on their spore load), but in the summertime, they usually live long enough to mate and lay eggs. This is why heavily infected populations like in Florida do not get wiped out by the parasite - because the infected, breeding monarchs can live long enough to continue the cycle.

Now, in terms of the collective population, OE has a number of detrimental effects, and these are still being studied. First, research has shown that a high local OE prevalence (like in a neighborhood) can reduce the local monarch abundance by as much as 50%. Second and more importantly, OE infections appear to have the biggest impact on the migratory phase of the monarchs, i.e. when the monarchs are attempting their long-distance fall journeys to Mexico or California. We often say that migrating with OE is like running a marathon with the flu. A lot (like tens of millions) of monarchs that attempt the migration will perish along the way. This is a huge conservation concern.

Testing monarchs for OE

First, let me make it clear to readers that the ONLY way to know for sure if a monarch is infected is with a microscope. Don’t let anyone tell you anything different. Now, as to how to do it, there are two ways. If you do own a microscope, you can do it yourself. It essentially involves holding the adult monarch in one hand, with its abdomen exposed (like in the top picture of this blog), and then placing a piece of clear scotch tape over its abdomen with your other hand. Then, you pull the tape off, kind of like pulling off a bandaid. This tape will then have a “sample” of whatever was on the monarch’s abdomen. You then stick the tape on a piece of white paper, and then look at the tape under your microscope for any OE spores, like the ones shown in the top picture. This whole procedure does not damage the monarch.

Now, if you don’t own a microscope, there is still a way - you can sign up to be a citizen science volunteer with the Monarch Health project, which is based at the University of Georgia (www.monarchparasites.org). That program was created to get volunteers to help monitor for OE in the North American monarch population. If you sign up to be a “tester,” they will send you a testing kit in the mail, which includes pre-cut clear tape, gloves, instructions, and other supplies (but not a microscope) needed. Then, you sample any adult monarchs in your area, following the steps above (placing the tape on monarchs). You then mail back the tape samples to the program headquarters, where their team will examine your samples for OE. They then report back to you, how many of “your” monarchs were infected.

Regardless of which of these you prefer, this author strongly recommends testing for OE, especially if you don’t know how prevalent it is in your own area.

OE has risen dramatically in the N. American population

This is something that everyone who loves monarchs must be aware of. Based on testing of living or archived (frozen) monarch specimens, the below chart shows this increase. This chart comes from a peer-reviewed study published in 2022, and since that study, I have been adding data to it.

Note that the prevalence of OE, historically, was less than 1%. Then sometime in the early 2000s, it jumped to over 10%. Put another way, it used to be that you would only see one infected monarch out of every 200 that you caught; nowadays, one out of ten are infected.

Keep in mind that this graph is based on the main, eastern part of the North American population, which makes up 99% of the collective monarch population. For the much smaller, western cohort, the OE prevalence there is higher (30-40%), though it seems to have always been higher, i.e. it has not risen.

Where are the OE hotspots?

This is a question best answered by looking at the aforementioned Monarch Health program results. Their website has a nifty mapping feature, where they add each volunteer location to a map, and color code each dot based on the prevalence of infections within those monarch samples. Below is a screenshot of the map. Note that if you want to zoom into your region, you should go to the actual map page on the Monarch Health website.

I usually remind people that if this map were made 30 years ago, all of the dots would be blue.

From this map you can see there are some serious OE hotspots right now, which are all of Florida, southern California, and parts of southern Texas. Also, if you zoom in you can see that many areas along the Gulf coast, like New Orleans, are growing hotspots. Note that the areas with no dots simply means there is no data. It does not mean these are OE-free areas. Also, for the people elsewhere in the range, you are not home-free. You DO have OE in your region, and don’t let anyone tell you differently. The prevalence varies from place to place and from year to year. The BEST way to know what your local OE prevalence is, is to test some wild monarchs in the region.

If you ARE unfortunate enough to live in an OE hotspot region, you are in a tough spot, because most of the monarchs flying into your yard are infected and dropping OE spores on all milkweeds in your yard. In fact, the situation is so dire in Florida, that I have recommended that Floridians not plant any milkweed in their yards. See that blog post here. People in southern California should also consider this, and the same goes for anywhere else where the local OE prevalence is over 50%.

OE and milkweed

OK, so I’ll add this section in here because there is a lot of misinformation about it. First, recall that OE spores are transmitted when infected adult monarchs scatter OE spores onto milkweeds, then the monarch caterpillars eat the spores, which starts a new infection. So, this means that any milkweed can technically become a source of a new infection. However, non-native milkweeds have a tendency to remain in leaf longer during the season in most areas, so that they can build up OE spores on their leaves. This is why they have a higher chance of being a source of infection. In areas where they never (or rarely) die back, like Florida, southern California or southern Texas, their leaves basically end up being a Petri dish of OE spores.

You might have heard that to “fix” this, you can simply cut back any non-native milkweed. That’s bullshit. Cutting back milkweed, especially in a high-prevalence region, simply delays the next transmission cycle. It in no way “fixes” the problem. Once the cut-back plant regrows its leaves, it will immediately get OE spores deposited on it when the next monarch comes along.

Again, if you live in a high-prevalence region, you cannot have milkweed without adding to the infection problem. And, if you don’t know if you are in a high-prevalence hotspot, then learn to test the monarchs you see in your region.

Can it infect other butterfly species?

The answer here is yes, and no, and “we don’t know yet.” First, we scientists have always known (or thought) that this parasite does affect other close relatives of monarchs, like those in the genus Danaus. Those that come to mind are queens, soldiers and African tigers. But, then there was a stunning discovery in 2020 of OE in some odd Lepidopterans that aren’t at all related to monarchs, and that circulate in the butterfly house trade, including an odd moth. This blew my mind and I wrote about it a while back in a blog. This discovery basically suggests that the parasite is NOT simply restricted to the Danaus genus, like we all thought.

So, the jury is still out on this question.

Important links for more learning

I’m going to keep adding to this list in this section, but for now, here are my top three links you need to visit next in your learning journey.

• Monarch Health project website - www.monarchparasites.org

• Prior MonarchScience blog describing the OE increase - link here

• Peer-reviewed study describing long-term trends in OE prevalence - link here

Thanks for reading!

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The first study was from a group of researchers from the University of Cincinnati, published in 2022 in the journal, IScience. A link is here. This project was focused exclusively on the effects of light on ADULT monarchs, and, on how the light affects their orientation ability during migration. The authors reasoned that even though migrating monarchs only fly during the day, they still are exposed to nighttime light if they happen to be resting on trees in urban areas or near streetlights. Being exposed to light when they need to be resting could affect their internal compass, or other physiological bodily functions (stuff we humans can’t see).

To help visualize the magnitude of this issue, the authors included the below figure in their paper, which shows just how much artificial light there is in the fall migration flyways.

There were a number of experiments in the study, and they all involved assessing how monarchs perform in a “flight simulator,” which is an apparatus where a monarch is harnessed in a washing machine sized tub, and they can flap their wings to orient themselves in whatever way they wish. In the region of Cincinnati, monarchs should be orienting to the southwest.

I’ll also note that the authors used wild-caught, fall monarchs for the experiments.

The part of the study that is most important is the experiment where they placed monarchs in the flight simulator at night, and in a dark room. They report that all monarchs essentially remained quiescent while hooked up to the device in the dark (sort of like sleeping). Then, the researchers turned on a bright light near the simulator, which simulated sunlight. They report that 96% of the monarchs immediately began flying, and, in the proper southwest direction!

The implications from this finding are that the monarchs can’t differentiate artificial light from natural light. The authors stated that they don’t think that the lights actually trigger roosting monarchs to begin flying at night, but the light probably does influence their circadian rhythm (their internal “clock”), which they use to help them know which direction to follow depending on the time of day or the stage of the migration.

OK, next I’ll describe two projects that examined how artificial light affects monarch LARVAE.

The first of these projects was from a group of researchers from the University of Virginia, and the paper was published in 2023 in the journal, Basic and Applied Ecology. A link to it is here. The goal of the study was to understand how artificial light affects the growth of common milkweed, plus, how it affects any monarch larvae feeding on that milkweed. The experiments were conducted in a greenhouse, using potted plants, and they had had rigged their greenhouse with LED lights above the treated plants that could be turned on or off, and, the lights were the same intensity as typical streetlights. They had programmed the lights to be on at night. There were other plants with no lights in a different room, and these simply got regular daylight.

For the larval experiment, the researchers placed very small caterpillars on the plants and let them feed until they pupated. They tracked how long they took to do that, plus how large they got. They also monitored how much time the larvae spent eating, both during the day, and at night.

The results of this project were interesting. First, there was minimal effects of the light on the growth of milkweed. But the lights did impact the monarch caterpillars. They found that the light-exposed larvae increased their feeding frequency compared to the controls. This was both at night, but also during the day! In other words, the artificial light at night made the larvae feed more. And interestingly, when the researchers weighed the pupae from the treatments, they found that the light-exposed monarchs were larger, though only by a little.

Now, this leads me to the OTHER project where researchers investigated the effects of light on monarch larvae. This one was published in the journal, Ecology, in May 2026, and it was conducted by researchers from Cornell University. Here is a link.

This was a field-based project that was conducted over two years. I’ll place a figure from the supplemental file below, which shows their setup. It looks like they had large outdoor mesh cages with potted milkweed plants in them, and each plant itself had a mesh cage around it. Some of the cages had led lights above them, and some did not. Then, the researchers placed monarch larvae on each of the potted milkweeds, and tracked their growth.

The results here were similar to the greenhouse project. The researchers found that the light-exposed monarch larvae grew faster and bigger. They report a 16% increase in caterpillar growth rates. On top of that, they had next measured the body and wing sizes of the monarchs when they eclosed. They report that the light-exposed monarchs also had larger wings, though this was only true for monarchs that had fed on common milkweed.

Ok, so what can we conclude from these three projects? From my read of them all, it looks like the effects of artificial light on monarchs are mixed. On the one hand, the lights might actually provide a helpful stimulus for monarch larvae, allowing them to grow faster and larger than they would under old-fashioned sunlight and normal daylengths. But on the other, the light exposure during the fall migration might not be a good thing, potentially disrupting their internal clocks.

As a scientist who studies physiology, I’ll also point out something that worries me here. So far, none of the studies have examined how light affects monarch metabolism, which is very important, given the extreme distance the migrating monarchs need to cover. Prior studies have shown that migrating monarchs have a surprisingly slow metabolism, which probably helps them by reducing energy expenditure during the flight. So, I’m worried because the faster larval growth we see here might NOT be a good thing because it suggests that the artificial light is elevating their metabolism. Perhaps the scientists reading this blog will take note of this and work on that next.

I’ll leave it there for now. If there are any new studies on the effects of artificial light on monarchs, I’ll be sure to update this post.

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Today’s blog entry is focused on a little-known report that was made available by the Xerces Society last year. I bet a lot of people reading this didn’t even know about it too. It is available online here. It was a summary of a very large statistical analysis of summertime butterfly count data, that was conducted by a large team of butterfly scientists. This team had assembled data from every butterfly monitoring program in the U.S. (there are dozens) and statistically analyzed the long-term trend (from 2000-2020) of each species of butterfly in the country. The goal was to determine which species are in trouble, as in declining, and which species are not, as in, increasing or stable. And, the team even went further, by showing how the abundance trends varied in different regions of the country.

Suffice it to say, that this report was extremely thorough, and it was meant to be a document that helps target conservation efforts toward the species that need it the most. Indeed, there were a lot of species that seemed to be declining. There were some that were stable though, and some were even increasing. For the purposes of this blog entry, I went through the document and figured out the trends for monarchs, which I’ll report below.

First, I’ll put a screenshot of the map presented in the report that shows the different regions they identified (I added monarch pictures to it).

Next, I’ll tell you the trends that they reported for each region, starting in the east. Note that if you are following along in the report, keep in mind that the trends for monarchs were not given in certain regions, so I had to look them up in another document. Apparently, the Xerces document only reported the trends if they were statistically significant, as in, if the species was increasing or decreasing. They did not report if the species was stable, which I found odd. In those cases, I was directed (by Cheryl Schultz, the main author) to find the trends in a recent peer-reviewed study that used the same data.

OK, so here goes.

In the Northeast, the monarchs are increasing. This trend was statistically significant and very pronounced. In fact, the data shows a 78% increase over the 2 decades.

In the southeast, the monarchs are also increasing. This was significant, and the trend was a 47% increase.

In the Midwest, there was no significant change detected. This is one that I had to look up in the other report. The statistical tests were close to being significant, but the trend was only a 6% drop in abundance over 20 years, which is meaningless. Monarch numbers fluctuate more than 6% from year-to-year anyway.

In the Mountain Prairie, there was no significant change detected. For the science nerds, the statistical model in this case showed a p value of 0.529. For everyone else, this means there was no change in abundance.

In the Southwest, there was also no change detected. If anything, the statistical model suggested a slight increase, but again, this was not significant.

The Pacific Northwest had no report for monarchs, and I believe this is because of a lack of data from that region that the team could analyze. There are fewer monitoring sites in that area of the country, and, fewer monarchs anyway. I will note however that Dr. David James recently performed a “non-conventional” analysis of all of the citizen reports of monarchs in that region, and he showed that there was no decline in these reports over 12 years.

In the Pacific Southwest, the analysis showed a statistically-significant decline in monarch abundance. The model showed this decline was steep, i.e. a 53% drop over 20 years.

So to summarize, the regional analyses showed that monarchs are doing really, really well in the east, they are more or less stable in the Midwest and central part of the country, and in the west, they are experiencing declines at least in the southern part, as in, California.

Regarding California, I’ll add some more context here. I just now looked at iNaturalist, to see the sightings of monarchs for this year alone (2026), and the below map is what came up. I circled the region of interest.

If you see what I see, then you’d be right to be confused over the reported decline in that region. I see two very red clusters of monarchs in California, which means, lots of monarch sightings. Remember, this map is just showing the sightings from this year. I guess it’s possible that those two spots were not included in the analyses, because there were no breeding butterfly surveys there. But either way, these two spots are troubling to me for a different reason. These are most likely, growing pockets of permanently-resident monarchs, which are growing because of people who plant non-native milkweeds. Ironically, people are doing this to provide “more habitat” for monarchs, which they have been told are in trouble. In fact, I’m even worried that if people in that region see this blog post, then they will even take steps to plant MORE non-native milkweed, thus perpetuating this cycle.

But ARE monarchs really in trouble in the U.S.? According to this report, they are not. Remember, the vast majority of monarchs in North America (99% of the population) lives east of the Rocky Mountains. And, in those regions, according to this analysis, they are doing fine.

Let me end this post by reiterating the main goal of the Xerces report, which was to identify butterfly species that are in trouble. It seems that there are a lot of species in trouble, but monarchs are not one of them.

That’s all for now.

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Hello blog readers,

Today’s post is another one of those “be careful what you wish for” storylines. That’s right, the Georgia Department of Natural Resources (DNR), is proposing to list monarchs as “Threatened” in the state. A news story about this is here. I’ll go over this move in the blog today, plus add my thoughts.

So this move is actually not very visible, and, it wouldn’t surprise me if you hadn’t heard about this until now. If you read the news story above, you can see that Georgia’s DNR is in the process of updating their “protected species list,” which as you might guess, is a list of all species in Georgia that are protected by the state, either as “endangered” or as “threatened.” There are hundreds of species on the list, and apparently, this list has not been updated in 20 years. Now it is about to be, and in the new update, monarchs will be added as “threatened.” The proposed new list is here.

Let me start by saying that I think this is a mistake. And I’ll point out here that I’ve reached out to the Georgia DNR to try to get more clarification on this, but have not heard back. From what I can tell, species are listed as threatened in this state if their numbers are declining or, if there is a risk that the species would be federally listed in the near future. Possibly, this second case was the rationale for the move, because the feds HAVE made lots of noise about listing monarchs nationally, although the current administration seems to want no part of it.

The reason I think it’s a mistake though is because all actual evidence we have shows that the number of monarchs in the state of Georgia in the summertime has been steadily increasing in the past 20 years. This was evident from the widescale analysis of breeding butterfly numbers in the Crossley et al. 2022 study (link here), and, a more recent analysis of summertime butterfly numbers by the Xerces Society also showed that monarchs are increasing across the southeast (link here). Increasing. As in, not in trouble, and certainly not threatened.

Ironically, I and some other scientists in Georgia were consulted a couple of years ago by the DNR to ask for input on the monarch status in the state, and I sure as hell did tell them this exact thing. But here we are. Why? Probably because of the never ending dogmatic public narrative about the “declining monarchs.” We’ve all seen this in the news almost daily, and, a LOT of people keep sharing these same stories. Comparatively, how many people reading this have shared either of the scientific analyses I mentioned above - that shows the monarchs are doing well? How many people even KNOW about those studies? If you didn’t even know about them, then my point is made for me.

The image in this blog post is actually from a news story from 2024 that also proves this point. The piece is titled, “Iconic monarch butterfly recommended for ‘threatened’ list as population shrinks” and you can read it here. It is from the Georgia Recorder and the piece describes how the monarch population is “dwindling” in Georgia. Note that this piece is actually describing the federal move to list monarchs as threatened, but the writer (like everyone else) simply assumed that this means the monarchs are dwindling everywhere, including in Georgia. Nowhere in the piece is there any mention of the ACTUAL numbers of monarchs in Georgia.

So here’s where it gets even more weird. Once a species is listed as threatened in the state of Georgia, it is then legally protected in the same way as if it was listed as endangered in the state. That means, no one will be allowed to collect or physically touch any monarchs in the state without a special permit from DNR. That’s right, Georgia will soon be another hands-off state, just like it is in California.

This last bit will have some major implications for a lot of people, including us scientists in the state. Once this legislation is finalized, it will become that much harder for us to conduct research on live monarchs. We will have to secure permits annually, requiring money (yes, they cost money) and our time.

People who captive-rear monarchs in their houses (or even outside their houses) will also be affected by this, though in this case, I’ll be happy to see an end to this dangerous practice. The people doing this may have their hearts in the right place, but there has been ample research now to show that captive-rearing is NOT helping monarchs. Click here to see a full list of studies.

In case you’re wondering, I did a little digging in the DNR pages to see what the “penalties” are for those who interfere with protected species in Georgia, and here is what I found. “In Georgia, capturing, killing, or possessing a protected species without a permit is generally a misdemeanor. Penalties typically include fines of up to $1,000 to $5,000, or up to 12 months in jail.”

So, if you capture or “possess” monarchs in any way in Georgia, you will (soon) be in violation of the state law, and, you could go to jail! Let that sink in.

I’ll update this blog post if I hear back from DNR, or if anything else changes in this story.

That’s all for now.

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Some housekeeping stuff…

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As I stated at the top, the findings from this project confirm my worst nightmare - that some of the monarchs that develop in Florida (more on this below) do indeed fly northward in the spring, and then become incorporated into the overall population. Why is this a nightmare? It’s simple - because Florida, and all of it’s milkweed, is now a cesspool of OE. It didn’t used to be, even back in the 1990s, but now it is, thanks to the millions of uninformed Floridians who planted non-native milkweed in the past 20 years. Nowadays, the infection prevalence in any given collection of monarchs there typically shows that 80-100% are heavily infected. (Note, before going further, if you don’t know what OE is, then read up on it here). What’s worse, this super-high infection level means that nearly every monarch that is flying around the state is dropping OE spores on ALL milkweeds they land on, or ever hover over. The OE falls from their abdomens like glitter. Then, when the hungry caterpillars consume the contaminated milkweed leaves, they then become infected, and then the cycle continues. I’ll put a screenshot from the MonarchHealth project below, which shows the insane infection prevalence there.

Let be back up a bit and cover some of the tracking project, based on my own read of the press release, and knowledge of the study sites. It sounds like this project was the brainchild of Dr. Ray Moranz, who is associated with Xerces, and who incidentally, worked with the late Lincoln Brower years ago in the late 1990s. In fact, they had collaborated on a project looking at milkweeds and queen butterflies in Florida (link here). According to the staff website, Ray is currently a Pollinator Conservation Specialist with Xerces, working mostly in the Midwest region.

So, in this project Dr. Moranz travelled himself to various places in north-Florida during the spring in the past two years, in order to capture some monarchs and outfit them with these new trackers. It sounds like Ray was aware that this question of where monarchs go in Florida is a pressing one, and so good for him for taking this on. In my prior blogging and social media writings, I’ve certainly wrung my own hands over this nightmare scenario too - what if the OE-infected monarchs in Florida actually fly north in the spring? My suspicions have only grown too, as in more recent years there have been some ominous-looking maps coming out of the Journey North program each spring, which appeared to show some early sightings of spring monarchs to the north of Florida.

Anyway, it sounds like Ray outfitted 16 monarchs with radio-trackers. And, if you have the monarch tracking app on your phone, you can see these tracked individuals, which are each labeled “Xerces28,” “Xerces37,” etc. I’ll put a few screenshots from my own phone below. Note that according to the press release, there were only 4 monarchs that moved northward out of the 16. So not all of them did. In fact, most simply wandered around the local area for weeks, and didn’t really go anywhere. But the important part is that these 4 were fresh-looking and new, meaning they had just completed their development locally (more on this below).

When you look at these maps, be sure to go back and also look at the map of OE prevalence above, and you can see why this is a nightmare-scenario.

Now, it sounds like all of the monarchs were checked for OE when they were first caught, though there is no other information given. Since the prevalence is so high down there, it would be surprising if these monarchs were all uninfected.

Incidentally, you may be wondering, if these were indeed infected monarchs, then how can they fly so far? I thought that the infection weeds them out during their migration (i.e. kills them)? It’s because we’re talking about the spring migration here, which is much different than the fall. In the fall, the last generation undertakes a ginormous 2-month trek of flying every day, non-stop. That is the insect-equivalent of a marathon. But in the spring, it’s more like a gentle jog, with lots of stops along the way, for seeking out milkweed. In other words, it’s not a strenuous journey. So, it makes sense that some infected monarchs could travel north. In fact, this is consistent with prior work by Flockhart et al. in 2017, who showed that infected monarchs do indeed fly northward just fine (they were not looking at Florida monarchs though).

Now, let me address something in the press release that is not accurate, i.e. that this discovery proves that Florida is an overwintering region for the main population, i.e. that it “receives monarchs in the fall, and produces monarchs that head north in the spring.” This statement carries some assumptions, which may or may not be correct, but which certainly require more research. First, this statement is based only on the appearance of the tagged monarchs. There were 10 of the 16 that looked fresh and new, and so Ray assumed that this meant that they were the offspring of monarchs that had wintered in Florida. But, these ALSO could have been offspring of monarchs that wintered in Mexico, and then passed through Florida on their return trip northward. In fact, when Lincoln Brower conducted his research in the same region back in the 1980s, his writing indicated that he believed that the Mexican migrants passed through Florida on their return trip, and laid eggs along the way. Lincoln had spearheaded a long-term survey of spring monarchs in this same region that Ray visited, conducting surveys of the same large native milkweed patch each week (pictured below). Their team found that (at least in the 80s and 90s), the monarchs “arrived” at this patch every spring like clockwork in April, stayed about a week and laid eggs, and then moved on. The eggs eventually developed into adults that also disappeared. The timing of all of this matched up completely with the timing of the spring migration from Mexico. I’ll put a screenshot of this famous milkweed patch below, which is called “Cross Creek,” near Gainesville. These are all sandhill milkweeds, Asclepias humistrata. Note that some of the tagged monarchs from Ray’s study are labeled Cross Creek.

Another very relevant bit of evidence comes from one of Lincoln’s grad students back in the 90s (Amy Knight), who had captured spring monarchs in this same region and then analyzed their body tissues to see what milkweeds they had consumed as larvae. Lincoln had pioneered this (crude by modern standards) approach as a way to estimate where monarchs came from in North America, and he called it “cardenolide fingerprinting.” Anyway, this student estimated that about 85% of the monarchs that came through the area in the spring had fed on common milkweed as larvae. Since that milkweed is what most of the Mexican-wintering monarchs consume, they reasoned that these monarchs were coming from Mexico.

So, can we say that this new evidence proves that Florida is a “wintering” home for monarchs? Yes and no. Yes, it is true that lots of monarchs arrive in Florida each fall from points as far north as New England, or even the Midwest (we have tagging evidence, findings from stable isotopes, and even bluetooth tracking evidence). Some of these monarchs remain in Florida, never to leave. Some keep going southward on to Cuba (never to be seen again). But do ANY of these (formerly migrant) monarchs remain in Florida all winter, then produce offspring in the spring that “remigrate” northward? This is what the press release is implying. In reality, we don’t know that yet.

For now, it may not be as important to know whether these monarchs were the offspring of Mexican migrants, or Florida-wintering monarchs. What IS important is that these monarchs had “grown up” on milkweed in Florida, where the OE prevalence is sky-high, and where nearly every milkweed is contaminated.

That brings me to another dubious claim of the press release, which was that the findings prove that natural patches of milkweed in Florida are less prone to OE contamination. Again, there is previous little other information given to verify this, but I will point out here that the sample size of this study was n=16. That is just not enough to make any claim whatsoever about habitat quality, infection prevalence, monarch fitness, etc. So again, we really don’t know yet if any landscapes in Florida are “safe” from the OE onslaught. It is important to keep in mind here that most research shows that monarchs can wander for miles during their breeding lifetime, meaning that a monarch that develops on a contaminated milkweed patch in an urban yard in Florida can easily later fly over to a native milkweed patch nearby.

All I know is that this is a day that I hoped would never come. That we find out that Florida’s cesspool is not “contained” within Florida.

Let me end with these thoughts. There is a tragic irony here for Xerces, who has for years, been pushing the “save the monarchs and plant milkweed” trope, and which Floridians have responded to, only with non-native milkweed! Now, Florida is overrun with OE, so much so that I actually recommend that people in Florida get rid of ALL of their backyard milkweed so as to keep from adding to the infection problem (I blogged about that here). The fact that someone from Xerces now discovers that the monarchs from Florida can move northward, potentially carrying their infections with them, is the tragic irony.

That’s all for now.

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Hello blog readers,

Today’s post is about a study that examined, among other things, how monarchs “decide” to become the super-generation that undertakes their long-distance migration in the fall. I put the word decide in quotes here because it’s not necessarily a decision per se, but this does convey the idea to us humans. Basically, the last generation of the season is the one that we call the “super-generation” because these monarchs are special - they actually undertake some physiological changes that help them with their long-distance migration. One big change is that their “private parts” (reproductive tissues) are not yet formed in the adult stage. We call this reproductive diapause. This makes their bodies significantly lighter, which helps them fly better during the migration.

Over the years there have been many research projects that have looked into the conditions needed to trigger reproductive diapause, and there is a laundry list, because it seems like any one item can be a trigger, though we think that all of them combined make the best trigger. The list includes 1) cool fall temperatures, 2) declining daylength, and 3) milkweed senescence. One big question that scientists have had though is exactly WHEN do they make this decision during their lifetime - is it after they eclose and feel the wind on their wings, so to speak, or is it when they are munching on milkweed as fat caterpillars? Well this study in question found the answer, and it is in the caterpillar stage.

The paper was published in 2025 in the Journal of Insect Physiology, and it was conducted by Samuel Stratton and Andre Greene at the University of Michigan. Here is a link. This study appeared to be about more than just this question though. The researchers were taking a deep dive into what happens to monarchs after they enter the diapause stage, as in, which genes get turned on in their brains! But, as part of this project, they had first made the discovery about the diapause decision, which is what I’ll focus on here.

They way they did this seemed pretty straightforward, though it required a lot of setup and time. They essentially reared a whole bunch of larvae in different conditions to see which ones turned into monarchs in reproductive diapause. The first was a control, which was meant to be exactly what normally happens with wild monarchs at the end of the breeding season. They reared some caterpillars completely outside in an “insectary” which I think means a mesh tent, and during the fall. These caterpillars were fed common milkweed until they pupated, the pupae remained in the insectary, and after they eclosed the adults remained in the insectary for 10 days. So, this treatment was fully outdoors. Next they had one treatment where the caterpillars were reared in an incubator that was set to mimic fall-like conditions (cool temperatures, declining daylength). Then, when these caterpillars eclosed, the adults were moved to an outdoor insectary for 10 days. This treatment was to sort of like a second control.

The other two treatments were where it gets interesting. In one, they reared some caterpillars in an incubator that was set to summertime conditions (warm, lots of light), and these remained in the incubator for 10 days as adults too. Then, there was one treatment where they had reared some caterpillars in the summertime incubator, but then after they eclosed, they were moved to the outdoor insectary (in the fall) for 10 days. This last one is the most interesting. Essentially these caterpillars were tricked into thinking it is summertime, but then once they became adults, suddenly they were experiencing fall conditions. Would that be enough to turn them into migrants?

It turns out, the answer is no. The researchers had carefully examined the monarchs from each treatment, to see if they were in “reproductive diapause.” Unfortunately, the best way to do this is to dissect the females and look at her insides to see if she had any mature eggs. Those in diapause do not, or at least, they have very few mature eggs. So, the researchers did this for all treatments, and the results are below. This is a figure from the paper, which I’ve modified slightly to ensure readability.

When looking at this graph, keep in mind that the females with LOW counts of mature eggs are in reproductive diapause.

So, their results for this part of the project clearly showed that monarchs reared completely outdoors (dark blue bar) developed into reproductive diapause adults, as did those reared in fall-like conditions in their incubator (light blue). This was expected. Then, larvae reared in summer-like conditions all the way did not (red bar), also as expected. These larvae turned into adults that were developing eggs, which means they were getting ready for breeding.

The most important finding here though was that the individuals reared in summertime conditions, but then transferred outside as adults (yellow bar), also developed eggs. This here is the proof that the monarchs are making the “decision” to be either breeders or migrators, in the larval stage, not the adult stage. Even though these adult females were experiencing fall conditions for 10 days after eclosion, they were still developing eggs, because they “grew up” thinking it was time to breed. As mentioned at the outset, these adult monarchs would be poorly-suited for long-distance migration because of the weight of these eggs alone.

Now you might be thinking that this last treatment does not seem realistic - when would larvae experience summertime conditions but then jump into fall conditions? Well this does happen, as in, when people rear monarchs in captivity indoors. Even though scientists (like me) have told these people over and over again to stop doing this, there are still thousands of folks who do this, thinking they’re helping. Well, they’re not, and this piece of evidence proves it.

Think about it for a second - rearing monarchs inside a home essentially subjects the larvae to some of the same conditions as those in the summertime treatment above, since there is prolonged, artificial light, and a warm environment (most people don’t allow their indoor rooms to go down to the 40s and 50s at night). Then, when the larvae eclose into adults, they are released outdoors, straight into the fall conditions! Guess what, if you’ve done this, then you’ve released monarchs that did not properly develop into migrants.

Note - for the monarch-rearers reading this: please don’t just take this to mean that as long as you simply move your caterpillars outside, you are fine. You’re not. There are still other issues with captive-rearing that are problematic. Just stop doing this altogether.

Getting back to the paper, this finding now begs some more questions about exactly HOW the larvae are making this decision, and, what physiological changes are occurring in the larval or pupal stage that triggers the diapause. So, there seems to be a need for more research here. But, this is what we say about any good scientific study - it should give you answers, but then open up more questions.

I’m going to leave it here for now. Thanks for reading.

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Take a close look at the photo above, and look closely at the monarchs, which are presumably all migrants in a fall roost. If you can’t tell, very few of these are females. This is something that often gets noticed and reported on every fall, actually, which is weird. Especially when you consider that whenever people rear monarchs in their homes, or when scientists rear them in the lab (even in the fall), the sex ratio is always pretty much 50-50. And in the summer when you catch breeding monarchs, the sex ratio is also pretty even.

This is actually not a new thing and it’s something I’ve been following with interest for a few years now. For some reason, when you look at collections of migrating monarchs (either tagged ones or from photos like the one above), you see far more males than females! In fact, in most large collections of migrants these days, males outnumber females by 3 or 4 to one. As scientists, we have no idea why this is occurring, or even if it’s a bad thing!

One thing that we do know is that whatever is happening to female monarchs during migration, it’s happening more so now than it used to. A number of years ago, I worked with Eduardo Rendon, of WWF Mexico (who coordinates their overwintering program) on a paper that described how the sex ratio of monarchs overwintering in Mexico has been slowing shifting in the past 30 years, going from 55% females in the late 70s to 45% females in recent years. We also reviewed the scientific literature on migrating monarchs, and found a similar trend was happening - in the last decade, males far outnumber females in migratory collections.

This paper got a fair amount of press, of course because it had the word ‘declining’ in the title:

Davis, A.K.* and E. Rendon-Salinas. 2010. Are female monarch butterflies declining in eastern North America? Evidence of a 30-year change in sex ratios at Mexican overwintering sites. Biology Letters 6: 45-47.

A link to the full paper is here.

Here is the main figure from our paper, showing the decline in females at the overwintering site:

So, for some reason, there are far fewer females seen migrating than males, and, this trend seems to be getting more pronounced with time, and, it is leading to a very skewed sex ratio at the winter colonies. That is the big mystery.

I know what you’re thinking, and we already have an answer - this trend does not seem to be because of different ‘catchability’ of males vs females during migration or at the overwintering sites. In a paper I did in 2010 with Billy McCord, a dedicated tagger from North Carolina who has loads of tagging records, we found that only 35% of his 10,000+ tagged monarchs were females, and importantly, that number was the same whether you looked at monarchs he caught flying, or caught roosting. So because females still were scarce in roosting clusters, this ruled out the catchability thing. In addition, previous researchers also showed females do not preferentially roost on different spots on trees than males do in overwintering clusters in California.

One thing I find interesting is that this skewed sex ratio is also being noticed in more northern latitudes, where the migration essentially has only just begun. This is very important, since it helps to figure out what’s going on, or at least, to rule some explanations out. At the time I was working on this issue, I had an idea that maybe the females simply experience higher mortality along the flyway than do males (for unknown reasons). But, since these monarchs in the picture had presumably not been travelling for long, there should have been little mortality experienced thus far. In other words, if my idea held water, then you would see a 50-50 sex ratio near the upper end of the flyway, and a shrinking proportion of females as you go southward along the route. So I think the Michigan observation rules this out. In fact, it not only rules that explanation out, it really suggests that whatever is happening to the females, is happening before the migration even begins - like when the migratory generation is developing, perhaps.

One other thing to consider is that male and female monarchs do have inherently different flight ability (not flight behavior, per se). In a project I worked on years ago, we tracked flight performance of monarchs on a flight mill (basically a butterfly ‘treadmill’). We found females tended to fly for longer stretches than males - link here to see the paper. That COULD mean that females don’t need to stop as much as males to rest, and therefore we’d see fewer of them at ground level during migration. However, this inherent flight difference between males and females would presumably have been always present (i.e. ever since monarchs have been migrating), and it would not explain why this is a more recent phenomenon.

A more ominous explanation for this may be some inherent male-female differences in susceptibility to diseases and parasites as larvae. This is a stretch, but female caterpillars could be more susceptible to these natural enemies, and thus they may not survive to become adults in the migratory generation. We have a little bit of data from various laboratory experiments that supports this (females can differ in immune function and/or parasite load), but not a lot. We do know though that rates of OE always tend to be highest in the late-summer, so if this was the issue, it makes sense that it would have the strongest effect in the migratory generation. And, we also know that rates of OE have been increasing in recent years...hmmm...

As you can see, there are a lot of unanswered questions surrounding this very weird phenomenon. I don’t know of any scientists who are currently or planning to work on this question either, so this is something that may remain a mystery for a while. Until then, folks should continue to submit their observations of males and females to Journey North so that these can help us (scientists) figure things like this out!

That’s all for now.

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This post is about a paper that came out in 2015 that few people may have seen, but that deserves a lot of our attention in the monarch world. In the journal PLoS One, Nate Lemoine (the sole author) quietly published a study describing how the breeding range of monarchs will shift in the future because of warming climate. From a google search, it looks like Dr. Lemoine did the study as a graduate student at Florida International University. Here is a link to the (open access) paper - link, and a screenshot of the title is below.

There was no fanfare around this study. There were no reader comments on the paper at the journal website. The author was not someone known to monarch people, and he apparently did all of his work on his own. By all accounts, this paper slipped into the realm of publication without many people knowing about it. One person did - Elizabeth Howard, since the author used sightings from Journey North (with permission from Elizabeth), but beyond that, this was a fairly low-key study. However, the results of this work are anything but low-key. In fact, they have considerable implications for the future of monarchs east of the Rockies.

In reading the study, I could tell the author was very knowledgeable about the methods used (which I won’t get into here, but involved a lot of computer models). I also could tell that he was very thorough in his analyses and in describing the results. So all in all, this was a very good study, from my read.

The main question he addressed was how will the summer breeding range of monarchs change in the next 50 years (not sure of the exact time frame), based on the projected distribution of milkweeds. The idea here is that when the climate warms, the more northern regions (mostly in Canada) should become more and more suited for milkweed, and so the range of milkweed should expand northward over time. This same situation is happening with a lot of other species around the world (northward range shift), and this is basically what the researcher was testing in this study too.

Before going further, know that this study was conducted on a computer, using a very fancy program called MaxEnt, which is a program used a lot in the climate change world. To begin, in order to know how far the milkweeds will shift over time, he first had to train the computer program to know where they currently grow, and then the computer could “learn” the rest, like what are the maximum and minimum ranges of temperatures and precipitation (for each milkweed species), and day length, etc. that the milkweeds will grow in. He used current citizen science sightings of milkweeds, and their locations, to train the computer for this. Once that was done, he could then tell the computer program how the temperatures will look across the continent in the future, and then the computer can plot where the NEW milkweed range will be. Keep in mind that I’m purposely oversimplifying all of this here.

I’m going to jump right to the results next. Below are two maps from the paper showing where milkweeds (all species) currently are, plus where these milkweeds WILL be in the future (I think 50 years from now). I made this composite image out of two of the figures from the paper, and placed them side by side to make it easy to see the changes. Remember these are probabilities of occurrence, where the researcher predicted where they should be based on their known climate suitability. Look especially at the new range extending into Canada.

Another thing to note from these maps is how the range of milkweeds will EXPAND in the Pacific Northwest in the future. It looks like the monarchs in the west could even benefit from climate change, because their northern breeding range will expand!

After he figured out the milkweed changes, he then predicted where monarchs will be in the future (because monarchs are where milkweeds are), and the figure below shows the main result of that part. Again, this is a composite image that I made of two figures from the paper.

Note that the researcher did not examine monarch distribution in the west for this part, I think because of there being not enough records to train the program (at the time the paper was done). That’s why there are no monarchs “predicted” to live in California or the rest of the west.

By the way, he actually made two predictions for the future milkweed and monarch ranges - one assuming a moderate change in climate and one assuming a more dire climate change. From the paper: “The moderate scenario assumes that greenhouse gas emissions rise slowly until 2050 and decline thereafter, resulting in a moderate 1°–3° C increase in mean global atmospheric temperatures.” The severe climate scenario “assumes greenhouse gas emissions rise steadily through 2100, resulting in a more severe 2°–6° C increase in mean global atmospheric temperatures.”

In this blog post I’m only showing the results from the “moderate” climate change scenario.

Here’s my take - from looking at both the shift in milkweeds, plus the accompanying shift in monarch distributions, it looks like Canada is going to play an increasingly significant role in safeguarding the breeding population. It also means people who live in the southern United States will see fewer monarchs in the summer - not because they are disappearing, but because the monarchs simply moved northward. This is a really important point to keep in mind here - based on these findings, climate change is NOT going to result in a smaller breeding range, but simply a more northern one.

Here’s the really scary thing that is only barely touched on in this paper - When (not if) the breeding range shifts northward, that means the late-summer generation (the migratory generation) will need to travel farther each fall to reach the Mexico overwintering sites, and by extension, that means fewer and fewer monarchs will reach these sites. It would be like moving the finish line further back each year in the Boston Marathon and watching how the number of finishers goes down each year. Travelling farther means greater risks of storms, predation, road mortality, etc.

The bottom line from this paper is that climate change is going to change where monarchs breed in the summer (Canada), and this is going to have a huge impact on the overwintering numbers in Mexico. This is definitely a paper that folks should be aware of.

Thanks for reading.

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Today’s blog entry is about monarch wing size, which is something that monarch-lovers should know, and, be able to measure, because it (wing length) can tell you a lot about a monarch’s chances of successfully making it to Mexico.

First, let’s talk about monarch wing size. There are a few ways to measure butterfly wings, but the most traditional method is to measure the length of the forewing. Back in 2012, Tonya Van Hook and colleagues wrote a nice paper that described the best way to do this - the paper is freely available here - https://journals.flvc.org/troplep/article/view/89697. Below I copied one of the figures from the paper that shows how to measure the forewing length of a monarch, which is the distance (in mm) between the two red arrows.

Now that we covered how to measure wing size, let’s turn to its importance. Basically, the rule of thumb is the bigger the better for migratory monarchs, and we know this from a couple of scientific sources.

First, we know this from comparing different populations: back in 2010, I was part of a project that compared wing size of monarchs across multiple migratory and non-migratory populations. It involved examining and measuring many hundreds of monarch specimens from the eastern population in particular, and the average wing length there was 51.4mm. This could be considered “normal” for a monarch in eastern North America then, though keep in mind there is a range. The largest monarch I’ve ever seen had a wing length of 56mm I think. Conversely, the average of the non-migratory monarchs we examined (those from Florida, Peurto Rico, etc.) was less than 48.5mm. This is about a 3mm difference from the migratory monarchs. I know this 3mm difference doesn’t seem like a lot to us, but in fact, for monarchs this is a huge difference. So from this we concluded if you migrate long-distance, you tend to have big wings. This idea has since been backed up and replicated numerous times.

Second, by comparing monarchs within the migratory generation: in any migration season, you see there tends to be waves of migrating monarchs passing through a given site - some come early in the season, some in the middle, and then there are the stragglers. You probably know this if you do any tagging. The stragglers are the ones that fell behind the rest of the pack because they were too slow. Sometimes this is because of a random wing tear, but it also happens if they simply have small wings to begin with. Those monarchs at the front of the pack are the ones with the best flying gear and most energy - that’s why they’re at the front of the race. There have been a few studies over the years that have verified this by examining the characteristics of monarchs within the front, middle and last periods within a season. One was by David Gibo back in the 90s, which showed that stragglers tend to be small and the front-runners tend to be big. Another one was a paper I did with Dara Satterfield in 2014, where we also looked at wing sizes across the early, middle and late migrants, and we found essentially the same thing. The average lengths were 51, 50 and 48mm, respectively. This paper is online and linked here.

A couple of things jump out from the two paragraphs above: 1) non-migrant monarch wings tend to be 48mm or less, and 2) the straggler migrant wings are also 48mm. So it seems like a no-brainer that 48mm or less is a key number here. So what this means is that if you measure the monarchs in your backyard and their wings all end up being 48 or less, that’s a bad omen - they will most likely not survive the migration. On the other hand, if your backyard monarchs are all 51mm or greater, then you’re in business. If the monarchs are small, then they may not be getting enough food (too crowded maybe), or they may not have good growing conditions, or more likely, they are infected with OE.

The other thing to point out is that the importance of wing size probably depends a lot on where you are in the flyway. If you’re in the upper latitudes, like say, Minnesota, then it’s probably very important. Monarchs that start migrating from here have a long way to go, so they can’t have anything that slows them down (like having small wings). If you’re in Texas, it may not matter so much.

Finally, the other crucial piece of information to know is that there have been a number of researchers who have measured the wings of monarchs AT THE OVERWINTERING COLONIES. The majority of the monarchs there tend to be large, as in, with wings over 52mm in length! This in itself demonstrates the importance of having large wings to be successful in the migration.

That also means that if you find a monarch that big in your yard, then you know it is well-suited for a successful journey, no matter where you are.

So the take-home message for today is, wing size is crucial for migration success - the bigger the better (51mm or more). Now before I go I don’t want people emailing or posting comments saying ‘but I had a monarch that I tagged, UF4 5C3, or whatever, that had a wing length of 46mm, and it was recovered in Mexico’. That’s like saying I had an uncle who chain-smoked all his life (I actually did) and he never got cancer (he didn’t). That monarch, and my uncle, are statistical anomalies. Is smoking bad for you? Statistically speaking, the answer is yes. Just like the statistics say that small wings are bad for monarch migration.

That’s all for now.

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This blog post is about the future of monarchs in the eastern population. While there is a lively and ongoing scientific debate over the long-term population trend of this population (are they declining or not?), there is clear universal agreement amongst scientists that the future of the migration is uncertain. There are a slew of problems going against migrating monarchs - the overwintering sites are being continually degraded and logged (soon monarchs may not even recognize them!), climate change is predicted to extend the migratory journey, and last but not least, the rising prevalence of OE is rendering a lot of monarchs incapable of making the long flight. So with all these obstacles in front of it, there may come a day when the migration will cease, or at least monarchs will no longer travel to the Mexico overwintering site. If that happens, what would happen to the eastern population? That’s the question I’ll be exploring today.

Before you read too much further, first let me point out that this story is not all doom and gloom - if the monarchs stopped migrating to Mexico, it would not mean the collapse of the population. Monarchs in eastern North America will live on, but it would definitely change their biology however.

First, let me point out that some eastern monarchs have already stopped migrating to Mexico in the fall, and this number will surely grow in years to come, thanks to climate change. There are a growing number of sightings of adult monarchs staying in warm coastal locations in the southern and southeastern United States during the winter months. Just look at the Journey North reports for winter sightings in any recent year, and you’ll see lots. From viewing the notes on these reports it seems that these adults hang around butterfly gardens in backyards, or can be seen flying across beaches, or whatever. So far, no one has seen anything that resembles overwintering ‘clusters’ at these sites, i.e. with thousands of monarchs draping evergreen trees. So these sites aren’t really the same as the overwintering sites in Mexico, but the point is, the monarchs at these southern sites can survive the winter there. In other words, these sightings prove that adult monarchs can ‘overwinter’ in the southern US.

If a few monarchs have already figured out that they don’t need to go all the way to Mexico, how long will it be before the rest of them do? These places are only going to get warmer in the future. What I’m saying is that these winter sightings of coastal monarchs may represent the early stages of future overwintering sites, that may one day resemble the western overwintering sites in California. If you look at the western population, those monarchs overwinter along the coastline of California at any number of places - some places have one or two clusters of a few hundred monarchs, some have tens of thousands. There are dozens and dozens of sites along the California coastline. This may be what we will see in the future at coastal locations in the southern US. With global warming soon upon us, it’s only a matter of time.

So what will this mean for eastern monarchs? Well for one it means not having to migrate as far! And this will surely result in changes to the way they look - they would get a lot smaller. I can say this with confidence because there is really good research showing how monarchs from long-distance migratory populations have larger wings than short-distance or non-migrants (multiple scientific studies report on this). For example, below is a picture of monarchs from the eastern United States (left), compared to monarchs from Puerto Rico (right), which don’t migrate. There’s a big difference in overall size.

Basically, the long-distance migration acts to keep the entire population big, as in, butterflies with big wings. The way it does this is by natural selection - each fall, only those monarchs with the biggest wings survive the journey, and small-winged monarchs usually don’t make it (big wings are key for flying long distances). That means the big butterflies are the only ones that pass on their genes to the next generation in the spring. And this happens EVERY YEAR. So without this long-distance migration to weed out the small ones, the average wing size of the whole population would shrink over time. That’s why non-migratory monarch populations have small wings.

The second thing that would happen is that rates of OE would skyrocket. Based on the collective research around this parasite, populations of monarchs that don’t migrate tend to have very high levels of OE. Basically, long-distance journeys tend to weed out heavily-infected butterflies (just like it weeds out small monarchs), leaving behind only the healthy monarchs, and again, it does this EVERY YEAR. So every year, the entire eastern population gets a ‘spring cleaning’, and most of the infected monarchs are removed from the population. But without this cleaning, rates of OE increase dramatically. That was the conclusion of a paper by Dara Satterfield, that was published in a very good scientific journal (Proceeding of the Royal Society B). They surveyed OE levels in year-round breeding pockets of monarchs along the south coast of the US, and these populations (which were clustered around tropical milkweed) tended to have astronomical levels of OE - in some cases, 100% of monarchs were infected. These pockets can be considered microcosms of the entire eastern population, and they show what happens when monarchs don’t migrate - without the migration, we’ll likely see high levels of OE in the entire population.

So to wrap things up here, the loss of the migration would certainly be tragic, but it would not mean the end of monarchs in the east. But, without the long-distance migration to weed out the ne’er-do-wells, we would eventually be left with small, highly-infected monarchs. Don’t get me wrong, we would still have monarchs - they would just be different.

That’s all for now.

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Hi everyone,

Did that title get your attention? No? Does the deaths of millions of monarchs EACH YEAR get your attention? Ok now that I have it, let me tell you about a paper that scares the hell out of me...

There is a little-known paper in the realm of monarch research that I never thought got as much attention as it deserves. It was published back in 2001 in the Journal of the Lepidopterists’ Society, and it was a study conducted by Duane McKenna, Katherine McKenna, Steve Malcolm and May Berembaum. Here is a link. The title of the paper did not mention our beloved monarch, which is why it may have gotten overlooked.

This study was about road mortality of butterflies - in other words, butterflies killed by cars. This is a huge (and underappreciated) issue in North America, and given the recent efforts to enhance roadside habitats, and ‘butterfly corridors’ etc., plus having more and more cars on the roads, this is something that is only going to increase. Before this paper came out, there was virtually nothing in the way of scientific research on this subject, and the main goal of the study was to fill in this big gap. For this project the researchers attempted to quantify how big this problem really is (or was back in 2000).

Essentially the researchers walked along 13 specific roads in the State of Illinois on a weekly basis throughout one whole summer and fall, and they picked up all the dead butterflies they could find. The roads ranged from “country roads” to major highways, with speed limits between 35-65mph.

Each week they sorted the dead butterflies by species, or at least identified what group of butterflies they belonged to. The family Nymphalidae (which monarchs are a member) was one of the more abundant ones. If you’re wondering, the most abundant group of butterflies (by far) were those in the family Pieridae, which are sulphurs, yellows and whites.

Here’s the first scary bit from the paper: in the summer, the weekly mortality rate of all butterflies on the busiest roads was about 25 dead per 100 meters of road. The number was smaller on less-busy roads. That doesn’t seem like much, but the researchers then extrapolated these rates to the entire state of Illinois, which has “2050 miles of interstate, 276 miles of toll road, 14,892 miles of highway and 120782 miles of other roads” according to their research. They estimated that the total number of butterflies killed on these roads in one week in the summer was 20 million. That’s 20 million. In one state in the U.S. In one week.

Now for the monarchs. They found more dead monarchs during the fall, which they attributed to the monarch migration passing through the region then. In terms of numbers, they estimated that about 500,000 monarchs were killed during one week in the fall in the state of Illinois. That’s insane.

So that was just for one state in the monarch flyway, and for one week. But what about for the rest of the migration? A while back I did some back-of-the-envelope math to try to answer that question and to get a handle on the bigger picture, that is, how any monarchs die on roadways throughout the flyway and for the entire migration season. So to do this I took the estimate from Illinois and extrapolated it to the rest of the states that fall within the flyway. Essentially what I did was to take the total land area of Illinois (this can be looked up easily), plus the mortality estimate of 500,000, then I just scaled this up the the total land mass of all states in the central flyway. This assumes each state has the same amount of roadways (which they don’t), but I was only trying to get a ballpark figure here. Also, since that estimate was only for one week, I then assumed the migration takes about 4 weeks in each state to pass completely through, and I multiplied the whole thing by 4. I won’t bore you with the numbers from all of this, but in the end I came up with a staggering number of 25 million. That’s how many monarchs I estimated get killed each year on roadways during the entire fall migration. To put this into perspective, in recent years the number of monarchs at the overwintering sites in Mexico tends to be around 20-50 million.

I’d like to end on a high note here but I can’t.

This is VERY. SCARY. STUFF.

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Hello everyone,

In today’s post I’m going to delve into a study that is not necessarily about monarchs, but certainly does have relevance, and I’m pretty sure it’s something that monarch folks should know about.

It was published in 2015 in the Journal of Insect Conservation, and it was completed by a group of Canadian researchers - led by James H. Baxter-Gilbert, from the Department of Biology, Laurentian University (but now in Macquarie University in Australia). The paper has the ominous title of “Road mortality potentially responsible for billions of pollinating insect deaths annually”. Here is a link. The authors of this study basically attempted to quantify how many bugs get killed by cars on roads, which is a lot like the study by McKenna et al in 2001 in the Journal of the Lepidopterists Society, that I discussed in a different post - although for some strange reason, the authors of this new paper did not cite the McKenna study - clearly an oversight.

This study took place in a fairly remote section of Canada, in central Ontario, along a 2km stretch of the Trans-Canada highway. For the folks who aren’t familiar with this part of the world, I can paint you a picture of it - I’ve travelled this road myself in years past. This part of Canada is mostly flat, and is mostly wooded, with scattered openings of rocky barrens or bogs. There are few towns or other signs of people - in fact, this study took place on a section of highway that passes through a First Nations Reservation, which just means the area was basically untouched wilderness. I might add there are no old fields full of milkweed, or even any farmland at all. It’s just rocky wilderness. But there is a steady stream of car traffic through this road, since it is a major thoroughfare for people travelling east or west through Canada. The authors cite information from the Canada government that says about 9700 cars travel this road each day. so it’s definitely a well-travelled highway, despite the remoteness.

Here are a couple of pictures of the side of the road from this section of highway, which I downloaded from google maps (just do a google search for Magnetawan First Nation and look at the satellite view or to get photos). You can see that there is not much there. I’ll explain later why I’m going to so much trouble to describe this location. Apparently these pictures were taken in the summer too.

So the methods of this study were much like the 2001 McKenna study; the researchers walked this 2km stretch of road throughout the summer months (over two years - 2012 and 2013) on a regular basis, picking up dead bugs on the side of the road. These guys were very thorough too - they collected everything they found, even the wasps and flies. At the end of the censuses they sorted out the specimens according to the type of bug it was, but they didn’t record which species they were. So at the end of each day they would have numbers like 47 flies, 56 Lepidoptera..., and so on. At the end of the study they basically just added all the numbers up to answer the original question (i.e. how many bugs get killed...).

The results for the number of bugs that were killed by cars on this 2km stretch of road were staggering. In one year there were over 4000 individual bees and wasps, over 8000 the next year. For Lepidoptera, there were about 2000 the first year and 2700 the second. The total number for all bugs in both years was 117,000 - remember this is just for one tiny stretch of road. Then, the authors extrapolated these numbers in a couple of ways. They came up with an average rate of mortality, per km of road, per day. For Lepidoptera, the rate was about 10 individuals/km/day. Then, they estimated how many bugs die on this one section of highway in Ontario, Canada, plus how many die on all roads in North America, which has 7,600,000 km of road, according to their information.

So, here’s the big numbers - based on their extrapolations they figured that about 500,000 Lepidoptera die on this one highway in Canada each summer, and about 9.3 BILLION Lepidoptera die on roads throughout North America each summer. Once again, this is a crazy number, and very scary. Incidentally, the authors did point out that this number is not very precise, given they were extrapolating a small sample to a much larger landscape, but I think we can all agree, the final number is likely in the billions - with a capital B. Maybe the most scary thing about this is that there’s not much we can do about this problem.

But speaking of this, here’s why I spent so much time describing this location, in the remote Canadian wilderness, and the answer has to do with our current conservation efforts for monarchs. As most folks know, there has been a big push to enhance roadside habitats for monarchs and other pollinators. But I wonder if this is such a good idea, now that these results are in (also the results from the 2001 study). Keep in mind that this Canadian study found tremendous mortality in an area where there was no habitat enhancement at all. It was just wilderness with a road cut through it. So what would happen if we made those areas even more appealing to butterflies? Given these new data, I would think the last thing we should be doing is encouraging more butterflies to take up residence near our roads.

So, I can’t really end on a high note here. Maybe researchers should just stop studying this issue so that we aren’t made aware of this problem - that might fix things.

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Today’s blog entry is about monarchs in the west, and how people’s gardening choices are messing with the migration there. I’m going to fill you in on a study that examined all of these issues.

The project was spearheaded by Dara Satterfield while she was a grad student of Dr. Sonia Altizer, and it was published in the journal Integrative and Comparative Biology in 2016. I’ll put a link to the paper here, but it may require a subscription to download. It was titled, “ Migratory monarchs wintering in California experience low infection risk compared to monarchs breeding year-round on non-native milkweed”.

Let me first set the stage for this paper. I’ll assume my readers already know about OE in monarchs - if not, you can find out more information about it here - www.monarchparasites.org.

So a lot of previous work has shown - quite convincingly - that long-distance migration weeds out most of the sick monarchs (i.e. those infected with OE) from the migratory journey, which tends to lower overall infection levels in migratory populations (this is a good thing). As a testament to this, in the eastern monarch population that has the longest migration of all monarch populations, infection levels have traditionally been less than 3% (but now they are much higher thanks to human intervention). But in populations that don’t migrate at all, infections tend to be high, because there is no ‘weeding out’ process. You might recall the previous paper by Dara, from 2015 - link here - which looked into the OE infection levels of those pockets of monarch that winter and breed in the southern US rather than migrate to Mexico. As expected, Dara found that most of these wintering monarchs were highly infected - 50-100% of the monarchs were sick with OE. Importantly, all of the places where monarchs were wintering in the US were places with tropical milkweed planted, so the connection was made between tropical milkweed and high OE levels. This plant tends not to die back in the winter in places where it doesn’t freeze, which allows them to build up OE spores on their leaves. Since the climate is warm, and there is year-round milkweed available, this makes monarchs want to stay and breed throughout the winter, instead of migrating to Mexico (or coastal California in the west). So because the monarchs lose their migratory urge, and also because of the high build-up of OE spores on the plants, this creates local hotspots of highly-infected monarchs - all because of tropical milkweed.

You may also recall all of the hoopla that ensued over these findings. Up until that time, people were joyously planting tropical milkweed, thinking they were ‘helping the monarchs,’ when in fact it turns out they were actually hurting them. I remember there was a flurry of press with crazy headlines too - the most high-profile one was “Plan to save monarch butterflies backfires“ in the journal, Science. I saw this one article getting posted and re-posted on facebook, and it is still being posted even now. I recall Dara getting some angry phone calls from people who read about the study, or who just read those headlines. I believe she was very diplomatic when she spoke with people - and I know she still is when she talks with the gardeners. This is certainly a very touchy subject with people - everyone just really, really wants to help monarchs by planting milkweed, and they sure as hell don’t want any goddamn scientists telling them they’re doing it wrong!

So the gist of the 2016 paper is very similar to the 2015 study, except that it was based entirely on western monarchs, i.e. monarchs in California. While the western population of monarchs doesn’t get as much press and exposure as does the famous eastern one, monarchs west of the Rockies do undertake an annual migration to and from wintering sites in California. It’s a shorter migration for sure, and there is much we don’t know about it, compared to the eastern one, but they migrate, nonetheless. We also know that western monarchs are prone to infections with OE. Historically, the levels had been much higher in the west, compared to the east - something like 30% of western monarchs used to be infected in any given collection of wintering monarchs, although lately the levels in the west have been way down - to less than 10%. So there should still be a ‘weeding out’ process during the western migration, similar to the east. We also know that more and more gardeners in California are planting tropical milkweed, and just like in the Gulf region, this creates local populations of year-round resident monarchs (non-migratory). So what does this mean for OE infection levels at these sites? That’s essentially what they tested in this new paper.

The way they did this was to gather ‘tape samples’ of monarchs from specific sites in California (see here for more info on the tape sampling method - www.monarchparasites.org). The sampling was done by the authors themselves, or from volunteers in the MonarchHealth and MonarchAlert programs. They specifically sampled monarchs at roosting sites during the winter - i.e. at those places along the California coast where monarchs cluster in the trees (these are migratory monarchs), and they also sampled monarchs at places where monarchs hang around all year - i.e. at sites with tropical milkweed (these would be resident monarchs). They also threw in a few sites where monarchs exhibit seasonal breeding. I posted a screenshot of their figure from the study below. In the end they sampled a total of 2135 migrant monarchs and 1290 resident monarchs, and I believe all of the sampling was done from 2013 to 2016. All of the tape samples were examined back in the lab at the University of Georgia.

So what did they find? You guessed it - the resident monarchs that hang around tropical milkweed all year all had very high infection levels compared to the migrants. About 3 out of 4 year-round residents were infected (74%), compared to only 8% infection rates in migrants (that’s like 1 in 10 monarchs that are infected). Statistically speaking, this was highly significant. This result is similar to what they found previously in the Gulf region, but in fact the California results are even stronger. So this paper leaves little room for doubt - if you plant tropical milkweed where it can grow year-round, you will have highly-infected monarchs.

Here’s another very important result of the study that folks should know about too. There were several (not many) tropical milkweed sites in the study where the homeowner had been cutting the milkweed back each fall for a few years prior to the study. This is a practice that was recommended to help keep OE spores from building up on the leaves. This recommendation was created to allow people to keep planting tropical, but to be able to feel good about it. But (big but here), when Dara looked at the monarch samples from these sites she found they were still highly infected - 72%! So cutting back the tropical milkweed did little to reduce the high OE infection levels at these sites! It seems that the problem is that there are just too many places with tropical milkweed, so that when a gardener in one neighborhood cuts back their tropical milkweed for the winter, the monarchs just go to the next patch down the block where the milkweed is not cut back. In other words, for the cutting-back thing to work, everyone has to do it.

So what should people do? Well, there are some big differences in opinions over this issue among the scientists I know. I know that before he passed, Lincoln Brower thought people should just rip their tropical milkweed out of the ground. Dr. Altizer and Dara have a slightly softer, more diplomatic, message - that folks ‘try not to plant it, and replace tropical with natives whenever possible’. I think I’m with Lincoln here. In fact, I’d say people should rip it out, and burn it for good measure. This plant just has too many strikes against it to justify keeping it around.

I’m going to end with this one final note - if you’re reading this now and you currently have tropical milkweed in your garden, you have some serious thinking to do.

Cheers

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In the fall of 2015, something very cool happened in the monarch world, and it happened without anyone knowing about it. A tagged monarch flew all the way from Nova Scotia, Canada to the overwintering site in central Mexico, a distance of 4,330km or 2,690miles. In this blog entry, I’m going to delve into this event in detail.

The person who tagged this monarch was Mr. Larry Bogan, who lives in a small town in Nova Scotia (very near where I’m originally from, actually). Larry has been actively tagging monarchs on his property for about many years, and apparently, this was the first of his tagged monarchs to be recovered in Mexico. Actually, Larry has become very involved with monarch conservation, and has become a resource for folks in that part of the Province. There was a newspaper article written about him in the Provincial paper (link here to see it). He even set up a website documenting his monarch adventures and providing background information on monarchs - I encourage my readers to check it out, particularly to view the pictures of his milkweed field, which is massive - link here.

The monarch in question was tagged in fall 2015 and recovered the following winter at the El Rosario site in Mexico. Larry himself actually didn’t even know about this recovery until the following year. The following is what Larry wrote about this on the Nova Scotia nature listserve (NatureNS), which is how I learned of his discovery:

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“I finally got around to checking the Monarch Watch list of tags found in Mexico for the 2015 season. We have been tagging for several years and have never had a return BUT this year one of our tags was retrieved in El Rosario, Mexico.

http://monarchwatch.org/tagmig/recoveries.htm (The El Rosario Butterfly Preserve is 110 km west Mexico City)

Monarch UGL-881 was released on 29 August 2015 from our home at Brooklyn Corners, Kings County, Nova Scotia along with four other Monarchs. It was a female. Her tag was recovered on 6th of March 2016. We had tagged four of the five Monarchs that day. All total we tagged 50 Monarchs of 75 raised last year. UGL-881 was the ninth Monarch we released last year and the seventh one tagged. Interestingly, our tags ranged from UGL-875 thru UGL-824 and UGL-881 was the only UGL tag found this year. The distance between our home and the El Rosario Reserve is a great circle distance of 4,330 km .

This answers some questions that we have had. Do our Monarchs go all the way to Mexico or head for Florida? Can they make it all the way to Mexico from Nova Scotia? Are we really contributing to the maintenance of the migration of Monarch?

This has encouraged us to continue our yearly efforts in raising Monarch above and beyond what can survive in the wild.”

********************

Andy here now - let me first say that I’ve met with Larry a few times and I’ve told him that raising monarchs in captivity is not good for the population.

So I find this tag recovery to be very interesting, because from my calculations, this could (and should) represent a record-setting migration. If you’ve been around the monarch community for a while, you probably know that the current official world record, which is recorded in the Guinness Book of Records, is ‘held’ by legendary tagger, Don Davis (though I guess the monarch Don tagged is the real ‘holder’ of the record). Don lives in Ontario, Canada, and has been tagging since the time of the Urquharts (the scientists who first developed monarch tags, and who’s efforts led to the discovery of the Mexican overwintering sites - though Lincoln always corrects me - they didn’t actually make the discovery). Basically, Don has been tagging forever, and apparently, one of his tagged monarchs was recorded in the Guinness Book of Records. BUT - I’ve always thought that the exact nature of that record is a little wonky though - you should read it for yourself before reading further, because I’m going to discuss it next - link here to see the record.

Now I love Don and all he does for monarchs, but if you read through that record carefully you can see what I mean about something wonky - the butterfly in question was tagged in Presqu’ile Provincial Park in Ontario (in the fall), then recovered in Houston, TX in the following spring. To calculate the distance this butterfly flew, they (not sure who) assumed the butterfly flew from Presqu’ile Provincial Park, to the overwintering sites in Mexico, then back up to Houston in the spring, for a grand total of 4,635 km (2,880 miles). I can think of two problems with this whole scenario - first, we don’t know for sure if this butterfly actually made it to Mexico that fall - it could have traveled only to Houston, stayed for the winter, and then no one found it until the next spring. Second, even if we assume the butterfly actually did make it to Mexico, the record people are really combining two journeys (fall and spring) into one trip to come up with the 4,635km distance.

The reason I’m going through all of this about Don’s monarch is that I think Larry’s monarch from 2015 has Don’s beat, if you really think about it. Because of where Don is located in Ontario, Don’s monarch would have traveled 3,429km (2,131miles) to reach the Mexico sites during that one fall trip in 1989. Meanwhile, Larry’s monarch from last year traveled 4,330km (2,690miles) during one fall trip - AND, we know for sure it reached Mexico. Below is a map comparing both journeys, based on the tag locations. You can see what I mean about Don being beat here - sorry, Don.

To be fair, perhaps this is just a matter of semantics - i.e. what do we consider an actual ‘migration’? Is it the complete journey all the way south, plus the return journey back - which is the original idea behind Don’s record? Or is it the one-way trip, in which case, Larry clearly has Don beat. If it’s the latter case (which I’m leaning toward), then what we have here is a new record for a one-way trip for a monarch. At least, this is the longest trip that I know of.

I’m going to leave it here.

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Get ready for some scary stuff in this blog entry. Today, I’m going to rehash the subject of roads and monarchs and pull together all of the evidence that I know of, including in the published and unpublished literature, and I’ll also tell you about some unpublished work I did looking into the issue of road-related mortality. As I alluded to in the title, this mini-investigation led to some very interesting findings that may make you question what you think you know about the decline in overwintering monarchs...

OK, here we go - roads and monarchs - I’ve blogged about this issue before, so you might want to refresh your memory before reading further. If not, here is a nutshell version of the prior blogs. In one case I delved into an older publication in the Journal of the Lepidopterists Society by McKinna and colleagues. That paper investigated how many monarchs were killed on roadways in Illinois per week during one year. Their estimate - 500,000, was staggering. In my blog I then took this estimate and extrapolated it to the entire fall flyway, for one full southern migration, and came up with 25 million. This is a rough estimate of how many monarchs die from being hit by cars in a typical migration within the United States.

The second paper came out more recently, and was even more scary. This one, by James H. Baxter-Gilbert and colleagues, in the Journal of Insect Conservation, examined how many butterflies and moths (all species) are killed each year in one tiny stretch of road in central Canada. Their estimate was 10 individuals/km/day. And they extrapolated their estimate to all of North America’s roads to come up with a staggering number of 9.3 billion - that’s how many butterflies and moths (all species) they estimate die on roads each summer and fall.

There was another piece of relevant evidence pertaining to the monarch migration that came out last year, and that was forwarded to me by Elizabeth Howard. This was not a scientific study, per se, but more of a observational report, and it was pretty scary too. It was written by a group of folks in the migration tracking project called Programa Correo Real- Mariposa Monarca, in Mexico. I’m not familiar with this group, but it looks like they have a facebook page (in Spanish) - link. Anyway, these folks wrote a report last fall about some observations on monarch mortality (among other things) on some roadways in Mexico, and included a number of pictures as well, of which I’ve copied the most pertinent here. In one specific part of the report, the observer, Rocio Trevino, said she was driving near Monterrey, MX at the end of October and witnessed monarchs being killed by cars and trucks (she actually saw them being hit). She also walked along the side of the road and counted dead monarchs. She estimated there were about 10 every 4 meters at one point (or 2.5 monarchs per meter). In one gutter in particular, which was about 20 meters long (pictured below), she picked up 115 dead monarchs (74 males, 41 females). This is about 5.7 dead monarchs per meter. From what I can tell from reading the report, she made similar observations on a number of other roadways.

So this report was pretty scary. To demonstrate just how scary, let’s do some quick math on these numbers to extrapolate it to the entire Mexican flyway. And keep in mind this is very hand-wavy, back-of-the-envelope stuff. The high ‘rate’ of mortality from this report (5.7 monarchs/meter of road) would translate to 5700 dead monarchs per km. There are about 377,000 km of roads in all of Mexico (based on a simple web search I did). From looking at a map of Mexico, I would guess that only a quarter of these roads are within the monarch flyway in Mexico, so that leaves about 94,250 km of roads within the flyway. By extrapolation then from the 5.7 number, the number of monarchs killed on roads in Mexico is about 537,225, or about half a million. Now recall that this observation was based on only a single day, so if we want to know how many monarchs are killed on Mexico roads during an entire fall migration through that region (we’ll assume it’s about 1 month), then we multiply this number by 30 to get 16,116,750 - about 16 million. NOTE - in a previous version of this blog post I had made an error in this calculation, but I’ve fixed that now.

Now this estimate for Mexico could be off by a few million, but no matter how you slice it, it seems clear that the amount of road mortality in Mexico is pretty substantial.

So let’s recap - we have a project done in Canada that shows millions of butterflies are killed on roadways each year, we have a project from the United States that shows millions are killed each year here, and we have evidence from Mexico that shows millions are killed each year there too. Collectively, it is easily possible that over the span of the entire fall migration, the death toll from roads on the monarch migration is anywhere from 30-50 million. When you consider that the overwintering colonies in Mexico contain about 50-100 million monarchs in recent years, it really hits home just how massive this problem is.

OK, are you scared yet? Wait till you see what’s next - So, I got to thinking a while back, if cars are killing such a huge amount of monarchs each year, would the number of cars on the road be related to the number of monarchs that reach Mexico each year? In other words, could the decline of monarchs in Mexico be caused by an increase in vehicle traffic on our roads? To answer this question I tracked down information on the number of registered vehicles in the United States per year (I didn’t look at the other countries). I found these data online here at the US dept. of transportation. Unfortunately, this is a count of all vehicles in all states, and I couldn’t break it down by flyway region. But we’ll assume that the trends in vehicle abundance is the same in all states. Sure enough, it shows that the number of vehicles on our roads has steadily increased in the last 20 years. Meanwhile, as we know, the size of the monarch overwintering colonies has declined in that time frame.

So when you put the two datasets together, you get the graph below:

Crazy, right? From a statistical standpoint, I can tell you that these variables are significantly correlated (p<0.005). In other words, there is a statistical association between these variables, so that as one goes up (vehicles), the other goes down (monarchs).

From looking at this graph, you may also be thinking this looks familiar. It’s because this graph strongly resembles the one that supposedly ‘linked’ the monarch decline with the rise in roundup-ready crops - in that case, the crops have been increasing at the same time as the monarchs were decreasing in the last 20 years, and in that case as well, there was a significant statistical association, and the graph looked just like this one. So which one is right? Well that’s a good question. Correlations are frequently found in science, but most scientists don’t put much faith in them, because two variables (that sometimes have nothing to do with each other) can be correlated by random chance. For example, did you know that the number of swimming pool deaths in the US each year is correlated with the number of movies Nicolas Cage has been in? I kid you not. Look it up on the internet. The point is, correlation does not always mean causation.

With that said, I think this vehicle graph does have something to say. At the very least, it demonstrates that the number of registered vehicles on the road has grown in the US, and likely in Canada and Mexico as well. And, it is abundantly clear from the available evidence I laid out above, that this can only be bad news for monarchs.

Bottom line - roads and monarchs don’t mix. In my opinion we should be doing everything possible to make roads and roadsides as unappealing as possible for monarchs and other insects.

That’s all for now.

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This blog post will be about something that seems to be happening more and more each year, that is, sightings of fall monarchs that seem to be still ‘migrating’ as late as November. Today I’ll tell you what you should do if you come across one yourself (spoiler - nothing).

So let me start by telling you about a sighting of my own, because this story will set the stage for the rest of this post. It was November 25 here in Athens, GA, and it was 74 degrees by mid-morning (!). This was much warmer than normal for here. On that day a monarch flew into my backyard. It stayed for a while, and I watched it land over and over again at the only bush with flowers remaining - all flowering plants in the yard had already died back for the winter. I eventually caught it with a net and had my son hold it for a picture. It was a female, and in pretty good shape - no wing tearing or significant fading, and I could tell that it was a migrant (as opposed to a local breeder, which we don’t have anyway) from its wing color (more on this later). In short, there was nothing outwardly wrong with her that would give away why she was here so late.

This monarch, and the weather, got me thinking about all of the other reports of late-migrating monarchs, and what this means for the future of the migration, as well as what people should do when they see or catch one. This last part - about catching them - is something that I know is going to sound harsh to some people, because I know there are folks out there who, when they find one of these stragglers, they’ll catch it and try to keep it alive over the winter inside, and let it go in the spring. There are even people who try to ship these to southern locations where they can be released in a warmer climate. While these people have good intentions, and these practices will likely help those individual monarchs, science tells us these practices could end up hurting the larger population.

Here’s the thing - these stragglers are not supposed to live. The monarch migration is a product of thousands of years of natural selection - each year, only the strongest and hardiest individuals survive the brutal 3000 mile journey to Mexico, and only these individuals live to pass on their hardy genes to the next generation. Monarchs that fail to make it to Mexico do not - this is natural selection, and it works every year to maintain a vigorous, healthy population. This is why the eastern and western North American monarchs are so much bigger than those in other non-migratory populations - because small monarchs in these populations tend not to make it to their respective overwintering destinations. This is also why eastern monarchs have the lowest prevalence of OE compared to all other monarch populations in the world - because infected monarchs don’t fly well and don’t live long enough to make the long trip. We have solid scientific evidence on both of these.

But, now that the climate is warming some monarchs that fail to reach Mexico actually do have a chance of surviving, and this explains the monarch I caught in November. This monarch either emerged too late or fell behind during the migration, and then became a straggler that would have surely died if the weather had turned cold, as it normally does this time of year. In fact, this year has been a poster-child for climate warming; the climate all over the flyway has been very mild, so that there have been a lot of sightings of late monarchs. So now that these late monarchs have a chance of surviving the winter, it is remotely possible they could even mate and lay eggs next spring - in other words, pass on their ‘straggler’ genes to the next generation. What this is doing is essentially removing natural selection from the equation.

Is this a bad thing? That depends. One could argue that the climate is warming, whether we like it or not, and this is changing the natural world in a lot of ways - the monarch is no exception. Monarchs could simply be adapting to this new environment by reducing their dependence on the migration for winter survival. Essentially, they could be learning that it is no longer necessary to fly all the way to Mexico in order to survive the winter. They are figuring out that as long as they can get to a state where it’s warm, they’ll be OK. On the other hand, this is probably bad for conserving the migration itself, which is something on everyone’s mind these days. If we truly want the famous monarch migration to continue in the future, it will be imperative for the monarchs (all of them) to maintain their migratory urge. In other words, the fewer stragglers in the population the better.

So what should a person do if they happen to catch one of these stragglers? If you haven’t figured that out by now, let me put it nicely - let nature take it’s course, please! By taking these individuals indoors, by shipping them south, by enabling them in any way, you would only be helping to speed up this growing phenomenon, where natural selection is no longer working to keep the migration going strong. If you love monarchs and want their migration to continue, do not foster stragglers.

Finally, so what about the wing color thing I mentioned earlier? I said that I can tell if a monarch is a migrant by its wing color. This is something I’ve done research on, and I’ll put a link here to one paper that is online, and that will explain this in more detail. Essentially, all of my research shows that migrants tend to have deeper orange wings than breeding monarchs do. Sometimes it is so deep that it looks brick-red. In the case of the monarch I caught last week, take a closer look at it below, and compare the orange of its wings to that of a breeding monarch on the left. The physiological reason behind this deep color during the fall migration is not yet clear, but we do know that migrants tend to be redder, and that redness is correlated with migration success. So, the color of the monarch that I caught tells me that it was indeed a migrant. However, since it was so far behind in the migration, it likely will not reach its winter destination.

OK, I think that about covers this topic so I’ll leave it here.

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That’s right, there are indeed many other critters in the world that are experiencing problems reaching their winter destination besides monarchs. A lot of this is due to either climate change, or human influence, or both. In this blog entry, I’m going to tell you about another critter that is also being similarly affected - the American Robin.

Let’s start by recounting what we know about global warming and what it is doing to monarchs, based on the available science. In a nutshell, the main thing is that monarchs are increasingly overwintering along the Gulf and southern Atlantic states of the US, instead of going to Mexico. Check out this map below, which was taken from the website of the Journey North program. This shows the locations where people have sighted monarchs during December and January for one recent year.

At these locations, it tends not to reach freezing temperatures, and adults can hang out there for the winter. As global temperatures rise, these places where it doesn’t freeze are expanding. So with each new year, these maps of winter sightings are showing more and more triangles. Some of this trend is being exacerbated by planting of tropical milkweed... but I won’t go there today.

It’s important to note here that these ‘overwintering’ sites in the US are not the same as the overwintering in Mexico - apparently, there is no clustering on trees, or any kind of dormancy behavior at all. The US-wintering monarchs seem to just behave normally - flying around, nectaring, etc. We know this because a number of years ago, I worked on a study that looked into this, which was published in the journal, Psyche - link. In the study, we documented the degree of wintering based on Journey North sightings.

The other big thing that is happening, or will happen soon, is that the breeding range of monarchs is (or will be) expanding northward. As the temps rise, the distribution of milkweed is expected to shift northward farther into Canada, and when this happens the monarchs will follow. There was a very nice study published about this sometime last year, which I blogged about. This northward shift can be good and bad - it will open up new areas for monarch breeding, but it will also increase the distance monarchs must travel to get to Mexico (if they choose to go there, anyway). This range shift is expected to happen in the next 50 years, and it may already be starting - a recent project I did with Elizabeth Howard from Journey North found evidence for a northward shift in fall roost sightings. This was in the chapter we had in the latest monarch book - Monarchs in a Changing World, published last year.

So with robins, the changing climate is also affecting their migration too, but in a slightly different way. Unlike monarchs, who are starting to shift their winter destination, a lot of robins are deciding to simply stay put at their breeding range for the winter - i.e. just deciding to not migrate at all. Let me go over some evidence we have for this.

First, some anecdotal evidence - my Facebook friend, Don Davis, just posted a comment about an increase in sightings of robins this winter up in Ontario, Canada.

Next, there is another program within Journey North where people track sightings of robins, and this program has also been recording increasing sightings of robins in the winter in the US and Canada. In the map below, the brown dots represent robin sightings in December. Note the brown dots in Ontario, Quebec and Minnesota...

And now for some evidence directly from a scientific study. A study was published in the journal called, Animal Migration, which directly looked at this issue. The paper was written by David Brown and Gail Miller, from Eastern Kentucky University - here is a direct link to the study. This journal is open access, so anyone can download the papers in it. As an aside, there are a couple of interesting papers about monarchs in the journal, if you look through the table of contents.

This paper examined the effects of global warming on migration in American Robins, by focusing on 80 years of band-recovery data. For the non-ornithologists out there, let me briefly explain these data. Ornithologists have been catching birds for decades as part of their research, and each time the catch one they place a tiny metal band on its leg that has a unique identification number on it. They let the bird go and if anyone every finds it again they can tell where it went, how long it took to get there, etc. It’s kind of like monarch tags, only there are a lot more people doing it, and there are a lot more data. For this project, Brown and Morris looked at all records of robins where the bird had been recovered.

I’m going to paste a figure from the paper that shows the all the points of capture and recovery for robins, joined by lines, which is pretty neat.

This figure has all of the records where there was a clear movement from the point of capture to the place of recovery. It indicates there are two main migratory pathways, one in the east, and one in the west (very reminiscent of the eastern and western monarch migrations). This is a very cool way to visualize the migratory pathways, although it does not get at the original question regarding climate change, and its effects on the migration. For this, the authors looked at the data another way. They looked through all of the recoveries and figured out which robins did not move very far from their breeding location. In other words, they figured out which robins decided not to migrate. Then, they looked at the proportion of non-movers (local recoveries) out of the entire sample, for each decade of data. Below is the figure for this.

Very neat - this shows that the number of robins deciding not to migrate at all has increased in the last 20 years or so.

So based on all available evidence, it is pretty clear that the American Robin is going through some changes to its migratory behavior, with the ultimate result being a loss, or diminishing, of its migration - sort of like monarchs. In fact, there are actually a lot of species around the world right now which are experiencing similar changes - a reduction in their traditional migratory behavior. Like the monarch, these species themselves are in no danger of declining, it’s just their migration that is diminishing. There was even a book written about this by David Wilcove.

Why am I telling you this about the robin and all of the other critters? I guess it’s because it’s important to understand that what the monarch is going through right now is more of a global phenomenon - it’s happening all over, to a lot of animals. And, a lot of it has to do with climate change. Knowing that the monarch is not alone in this gives some perspective about the scope of the issue.

That’s all for now.

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Some housekeeping stuff…

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Hello readers,

Today’s blog entry is about a question that gets asked over and over again - how fast does a monarch fly? I bet that everyone reading this has heard this question at least once, or maybe has wondered this themselves. It’s a question that pops up whenever there is talk of their migration, or of tagging, and I know that there are varying answers out there. In this blog post, I’m going to answer this question by looking at all of the available science on the subject.

For starters, the answer to this question really depends on whether you want to know how fast they fly - like, their actual flight speed, or if you want to know how fast is their migration. These are two different things. The migration consists of alternating flying and stopping to rest. And their flight speed is greatly affected by the wind conditions they are flying in as well. So considering all of this, it is perhaps no wonder that there are so many estimates.

I happen to be well-versed in this issue. In the 2015 book - Monarchs in a changing world - I and Elizabeth Howard had a chapter in it where we examined some Journey North data, and for that project we summarized all of the prior estimates of monarch flight speed and migration speed. So for this post, I’m going to essentially copy what we had in that paper and then add to it. If you have a copy of the book and want to verify my numbers, our chapter was titled, Tracking the fall migration of eastern monarchs with Journey North roost sightings: new findings about the pace of fall migration.” With this title, you can see why this project is relevant to the question at hand.

Let’s start with flight speed. The first estimate we have is actually THE first estimate, ever. Years ago (1960), Fred Urquhart published his book “The monarch butterfly”, and in it he described how he followed cruising monarchs with his car, and read the car speedometer while doing so. He claimed their flight speed was 18km/hr. If I sound skeptical about this, it’s because I am. As you will see, this number is much higher than other estimates we have. And, do you know how hard this is to do anyway? Fred also had made some other dubious claims too, like when he looked at monarch scales under the microscope he saw OE spores, and he thought were tiny scales!

Next we have an estimate from a very obscure study published back in 2001, by a whole family of citizen-scientists, I think (the authors were four people named Moskowitz!), who witnessed a large accumulation of monarchs and dragonflies during one fall migration. The study was published in the Northeastern Naturalist, and was titled “Notes on a large dragonfly and butterfly migration in New Jersey.” Apparently, the family was watching the insects as they crossed a parking lot on one exceptionally busy day, and they estimated their flight speed by timing how long it took to cross the lot, and then measuring the length of the lot. They got an average of 7km/hr for the monarchs.

Another estimate was from a paper I published back in 2002 in the American Midland Naturalist, with Mark Garland, who is associated with the Cape May Monarch Monitoring Project. Our paper was a report of some monarch observations we had made while tagging monarchs during the fall of 1999. At the time, Mark was tagging in coastal New Jersey, and I happened to be tagging at a site in coastal Virginia, just south of Mark’s site. That year, I captured about half a dozen of Mark’s tagged monarchs from NJ, and there was one in particular that was captured the next day. According to what I wrote in the paper, “monarch #182240 was tagged at Cape May on 6 Oct. 1999 at 13:00, and subsequently recovered at 17:00 the next day on Fisherman’s Island (the southern tip of coastal Virginia), approximately 16 daylight hours later.” Based on the distance from Mark’s site to mine (226km), and assuming the monarch flew only during daylight, we estimated it’s speed was 14km/hr. It should be noted though that there was a strong tailwind that day. If anyone is interested, I’ll put a link to this paper here.

One more estimate we have also comes from my own work, but this time in a laboratory setting. And this one is pretty cool. Have you ever heard of a butterfly treadmill? Well, in our lab we have one! It’s called a “flight mill”, because it measures butterfly flight speed. I’ll blog about this thing at a later date, but essentially, the way it works is you glue a monarch to a horizontal rod (it doesn’t hurt them), which is attached to a center post by a frictionless pivot, and the monarch flies in a circle around the pivot. A computer tracks the speed while it flies in circles. I know, it’s crazy, but this is actually a great way to learn about flight behavior in a lab setting, and entomologists use these things a lot. The monarchs actually fly for hours on this thing without stopping. If you want to see this device in action, there is a short video of it on youtube below. So a few years ago, I worked on a study that tracked flight speed in monarchs in relation to their wing characteristics. At that time we had examined over 100 monarchs on this flight mill and from these data we calculated the overall average flight speed of about 4km/hr.

OK, now for the migration speeds. Keep in mind that these estimates are very rough, because they rely on assumptions of how many hours monarchs spend flying each day. Also, migration speed is a lot different than flight speed because during migration, monarchs fly for a couple days, then stop for a day or two, then fly, etc. So this really should be called the migration pace or rate.

On the MonarchWatch website, there is a rough, back-of-the-envelope calculation for the overall migration rate for the entire fall migration. They figured the time it takes the fall migration wave front to go from Minnesota to the Mexico border (~2250km) is about 30 days, or 75 km/day. If you assume monarchs fly for about 10 hours a day, that translates to 7.5km/hr for the fall migration speed.

Next is another study I worked on years ago with Elizabeth Howard again. It was published in the Journal of the Lepidopterists’ Society in 2005. We examined spring sightings of monarchs travelling north, and we used a fancy GIS approach to estimate how fast the spring migration progresses. We came up with 70km per day. If you assume the monarchs fly for about 10 hours each day that translates to 7km/hr.

Finally, for the chapter we had in the 2015 monarch book, Elizabeth and I examined records of fall migration roost sightings from the Journey North program, and we specifically tried to estimate how fast the fall migration progresses, as it proceeds southward. I won’t bore you with the math here, but suffice it to say, we found the overall migration pace to be about 32km per day. In other words, with each passing day, new roosts are formed about 32km farther south than in the prior day. However, we did find some clear variation in this estimate. In the northern part of the flyway, the pace is about 14km/day, but as the migration proceeds southward, it picks up to about 42km/day. Again, if you assume monarchs fly for 10 hours per day, the overall average translates to 3.2km/hr.

So about the migration and flight speeds, let’s put all of the numbers together. We have a wide range of estimates that I went over in this post - 18, 7, 14, 4, 7.5, 7, and 3.2. Some of these numbers are based on direct observations of monarchs in flight, some are from looking at the entire migration cohort. I’m not sure we can say that any one of these is better than the others, so I would say let’s just average them all. So...the average of all of these numbers is 8.7, which we can just round up to 9. From my perspective (as a scientist) this average should be the most comprehensive and accurate estimate out there, since it is based on all of the science we have on the subject. Keep in mind this is an average, and there is clearly some variation to this estimate. In other words, monarchs are at least capable of flying faster than this, given the right conditions (like that strong tailwind in the tag-recovery story).

The most scientifically-accurate answer then, to the question, “how fast do monarchs fly?’ is about 9 km/hr, or 5.5 mph. To put this into perspective, the average person jogs at a speed of 6-8mph.

There you have it. Feel free to share this post with anyone who has ever asked you this question, and keep it ready to pull out in case you ever get asked again.

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Have you ever seen an odd-looking monarch caterpillar, and thought, I wonder if this is normal? How about a crazy-looking queen caterpillar? Well, today I’m going to tell you about two cases that I’ve been personally involved in where this happened, and where I helped to get these observations published in scientific journals.

First, take a look at this beauty - a monarch caterpillar. See anything unusual about it?

If you haven’t noticed it already, this monarch caterpillar has an extra set of tentacles on its 4th abdominal segment. Technically these tentacles are called tubercles in caterpillars. But whatever they’re called, they shouldn’t be there! Crazy, right? About 20 years ago, an undergraduate brought this to the lab from her parent’s house in Florida. Apparently, her parents had milkweed in the yard in Florida (tropical milkweed!) and when she looked for monarch larvae on them she came across this. I recall she eventually found some others (11 in all) and brought them in as well.

So I had not seen anything like this before. So I raised them all in the lab just to see what happened. I recall they all ate pretty normally, and eventually they formed normal-looking chrysalises, then turned into normal-looking adult monarchs - no extra legs or anything. They were a little on the small side for monarchs but otherwise pretty normal. I didn’t conduct any other tests on them, because I recall I was busy with other projects at the time. But I later helped to get the story published in a scientific journal - the Florida Entomologist. The link to the paper, which is downloadable - is here. Recall from previous posts of mine that I am a firm believer in publishing these kinds of observations, so that they are preserved for all time.

I never did figure out what was going on with these larvae. I suspected they were from a rare hybridization of monarch and either queens or soldiers, which also inhabit that region, and whose larvae have 3 tubercle pairs.

A few years later, someone found another monarch with extra tubercles and sent around a picture of it, which led to some more email discussion among monarch researchers, including Dick Vane Wright - the guy who literally wrote the book on milkweed butterflies. He had some thoughts on this, which I’ll share:

“I think it most parsimonious to assume, rather like eye-spots in marginal wing cells of adult nymphalids, that all segments of the larva, from 2 to 11 (with the possible exception of 4), have the potential to produce a pair of tubercles. However, within most lineages (species, species groups, subgenera) a given arrangement (formula) is normally stable -- and, given the observed possibility for variation, thus under stabilising selection. This then raises the issue, again, what are they for, what do they do? I guess we must presume that they have some ‘external’ adaptive function (anti parasitoid or whatever), rather than represent some ‘internal’, developmental constraint.…” -Dick.

I don’t recall this discussion moving much beyond that. Now I’m sure there are people out there who rear a gazillion monarchs in their kitchen each year and who have pictures of crazy-looking monarchs like this. Before you go sending them to me, let me tell you that this is something I don’t have a lot of knowledge about and that I wouldn’t know what to do with them! On the other hand, perhaps it would be nice to know how frequent this is, and if it is more frequent in reared monarchs vs wild ones, and if it only occurs in regions of the country where all three species (monarchs, soldiers, queens) overlap... hmmm...

OK, now how about a different case. Some time ago, a gentleman named Kip Kiphart from Texas (who has now sadly passed), sent me pictures of some crazy-looking queen caterpillars he and some folks found near Boerne, TX. Here’s one below.

Apparently, Kip and some of the volunteers at the Cibilo Nature Center had found some of these “red queens” (that’s what they called them, and it has since stuck) while surveying their milkweed patches back in 2010. They knew these looked different and so took some photos. Then Kip found some in his backyard that same summer. Then someone else saw some in 2013, and then again in 2016. So apparently they keep finding these in central Texas.

I worked with Kip to get these observations published in a scientific journal, and the paper was officially published in the journal, Tropical Lepidoptera Research. I’ll put a link to the paper here

We had a couple of goals for the paper: first we wanted to describe the caterpillars as best we could, and we included all of the photos. Second, we wanted to figure out if anything like this had been seen before, or essentially how normal is this? For this second part, we examined online photos of queen caterpillars that people post to their Flickr accounts, or blogs, or whatever. We basically just googled the words queen caterpillar. You should try this - it’s very illuminating. Then we went through each image and categorized it based on the color patterns. Below is a composite image we made for the paper. This image shows all of the “normal” color patterns for queens that we found. You’ll note that there are no red queens, but there is a great deal of natural variation in color patterns.

By the way, I obtained formal permission to use the photos above, and I’ll copy the statement from the paper that acknowledges the photographers.

“All photos were used here with permission. A. Round Rock, Texas (Joseph Kilgus). B. Scottsdale, Arizona (Gene Hanson). C. Pima, Arizona (David Bygott). D. Biscayne Park, Miami, Florida (Susan Ford Collins). E. Dallas, Texas (Dale Clark). F. Pima, Arizona (Michael J. Skinner). G. St. Catherines Island, Georgia (Christa Hayes). H. Thomas F. Riley Wilderness Park, Orange County, California (Jay Cossey).”

As you can see from the photos, there wasn’t a clear “normal-looking” image to go on. So in the end we concluded that that queen caterpillars just seem to have a great deal of NATURAL variation in color, and the red queens of Texas (that sounds like a song title!) just represent an extreme form of this variation. In other words, they’re not a mutant or anything. Maybe the folks in Texas can do some more digging into this and figure out what’s up with these red queens. Incidentally, I voted to call these the “Kiphart form” of the queen, but Kip voted me down (before he passed).

Well, I guess that’s it for today. I hope this blog will make you look more closely at the next monarch or queen caterpillar you see.

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Some housekeeping stuff…

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Greetings readers,

In this post I’m going to once again tackle that controversial topic that all monarch people know and love, tropical milkweed. If you are one of those people who still insists this plant is not harmful to monarchs, don’t bother reading this, because there is nothing in here that will help your cause. In this blog post, I’ll discuss some of the research coming from the lab of Dr. Jaap de Roode, at Emory University, where they study the monarch parasite, OE, and how this parasite is affected by tropical milkweed.

First, a few words about Jaap (pronounced “Yaap” - he’s Dutch). He was once a postdoc in Dr. Sonia Altizer’s lab back in 2004 to 2006 I think, and that’s where he got his start in the monarch business. Although I should say he is really in the OE business, since a lot of his and his lab’s research revolves around that parasite, as well as other parasites, like malaria. Jaap famously once said that he never cared much for monarchs before he learned they carry a cool parasite! So he is really a very exceptional parasitologist, who happens to study a monarch parasite. And his lab is very prolific - they have tones of scientific publications on OE, although a lot of these are very technical and not an easy read for the average monarch enthusiast. I’ll put a link to his lab website, where you can see for yourself how busy he and his people are - link here.

Back to the story for today - one of the most notable projects that Jaap has worked on and published was one where he described how female monarchs use tropical milkweed in a “medicinal” way. You may have heard news reports about this - here’s one from an online science news website, ScienceDaily. And, he has also even written a book describing how animals like monarchs “self-medicate,“ pictured below.

So let me explain this story more for the monarch folks, because I think a lot of people only read the headlines of these stories, and then they get a false impression about the whole thing, as in, they think that tropical milkweed is somehow good for infected monarchs.

Wrong.

To start with, tropical milkweed happens to have very high concentrations of cardenolides, the chemical compound that monarchs sequester internally and which is what makes monarchs toxic to predators. All milkweeds have this in varying concentrations. Tropical milkweed has the highest levels, or close to it. Let me come back to this point because it comes up later.

Let me also give some basic info on OE, in case there are readers who aren’t familiar with it - though if you are a monarch enthusiast, shame on you if you aren’t. This is a parasite that infects monarchs and related Danaid butterflies, and is is spread from female to offspring. Infected females have millions of OE spores on their bodies and when they lay eggs on milkweeds, some of these spores fall off onto the plant. The caterpillars then consume the spores when they eat the milkweed leaves, and then the infected caterpillars turn into adult monarchs, once again covered with OE spores. See Dr. Altizer’s page about OE for more info on this parasite - www.monarchparasites.org.

So Jaap discovered that when an OE-infected female monarch has a choice between laying her eggs on a low-cardenolide milkweed (like swamp milkweed) and a high cardenolide one (tropical), she tends to lay most of her eggs on the tropical milkweed. Then, he also discovered that when those eggs on the tropical milkweed turn into adult monarchs, their own OE spore load ends up being less than it would if the larvae grew up on swamp milkweed. So, Jaap reasoned that the infected females somehow know they are infected, and then they choose to lay their eggs on the milkweed that would most benefit their offspring - by reducing their infection severity. In case you are wondering, Jaap found uninfected females have no preference for milkweed type, so it only works if they are infected. So Jaap called this “trans-generational medicine” (or something along those lines), because the female (who cannot be cured herself) appears to be using the milkweed as “medicine” for her offspring.

So here’s the thing that a lot of people get wrong when they read about this project - the tropical milkweed does not cure the offspring, or even prevent them from getting infected. All it does is reduce the OE spore load on the infected offspring (i.e. the number of OE spores on the abdomen), and that kind of reduces their symptoms from the infection. Some of Jaap’s other research shows a very clear relationship between the spore load of infected monarchs and their lifespan - the more spores you have, the shorter your life. The idea here is that more OE spores means more damage is caused to the host tissues, thus reducing host lifespan. So if tropical milkweed reduces OE spore loads, that allows the infected monarchs to live longer. So make sure you understand this because it’s important for the next part. Remember, the gist here is that infected females prefer to lay eggs on tropical milkweed because it allows their infected offspring to live longer.

Here’s the reason why this is really, really bad - the last thing you want in your garden or habitat patch is for OE-infected monarchs to live longer! The longer they live, the more opportunities they have to spread their infections around, thereby raising the overall infection prevalence in the local population. So while the tropical milkweed actually is “medicinal” to the individual monarch, it ultimately leads to higher infection prevalence in the population! As if we needed another reason not to plant tropical milkweed, right?

So, why does tropical milkweed reduce spore loads of infected monarchs? Remember the cardenolide thing? Apparently, the high levels in tropical milkweed somehow interfere with OE replication. In fact, some of the latest work from Jaap’s lab (not sure if it’s even published yet) shows that infected monarch larvae that are raised on high-cardenolide plants end up with smaller OE spores. This is further evidence of how cardenolides reduce OE development internally.

OK, so that’s the medicinal milkweed thing in a nutshell. Perhaps in a future blog I’ll visit some of Jaap’s other work - he’s done some really nice research on the genetics of monarch populations - just fascinating stuff.

Hope everyone learned something new today.

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