top of page
  • Andy Davis

What to do with OE-infected monarchs that you raised - it's not that simple

Hello blog readers,

Thanks for tuning in to another edition of this crazy website-blog thingy! I hope this site has been useful to you in your own quest to help the monarchs using science. Today I'm going to talk about the OE parasite again. I've been giving this subject a lot of attention lately, because of the clear importance it has in monarch conservation efforts. I also hope that readers now believe this statement, likely thanks to the recent "game-changing" paper on OE prevalence. For anyone who didn't read that study, or my blog about it (link here), that paper basically shows that OE rates in eastern North America have risen dramatically in the last 15 or so years, which coincides exactly with the movement to "save the monarchs" in North America. It also coincides with the proliferation of tropical milkweed in gardens.

For a lot of folks out there, saving the monarchs means literally saving all of the monarch larvae in their backyard by bringing them into captivity. Let me briefly touch on this since it is relevant to this discussion. People who do this have their hearts in the right place, but this practice is not really saving the species, and it actually can do more harm than good if people take this too far and raise hundreds. Yes, you can in theory save those caterpillars from being eaten by predators, but in reality, this practice has not been shown to substantially improve overall population numbers. In fact, the subpopulation of monarchs west of the Rockies is a great example of this - if you look at their population numbers over the last decade, their population was steadily declining even as more and more people were raising them, but then the year after the state of California cracked down on home-rearing, their numbers immediately improved. Coincidence? Maybe, maybe not, but the point is, there was no evidence that rearing monarchs in captivity was helping to reverse the long-term downward trend there.

I get it - it feels good to release monarchs that you raised. And, it is amazing to watch the metamorphosis and show this to kids. This is indeed laudable. But, here's the bad news. Those same monarchs you released could be infected with OE (since many infections are asymptomatic), and now, you've just released a bunch of infected monarchs into your garden, and then, the subsequent larvae from your milkweeds will also be infected. This scenario would clearly be harming the monarchs in your backyard, which is the opposite of the original intention. And more importantly, there is every indication that this is one of the factors behind the dramatic rise in OE rates nationally. In fact, a survey done by Chip Taylor found that over 85% of people who rear monarchs do not test for OE!

OK, so let's get to the crux of this issue. Let's say that you did rear a few monarchs, with the best of intentions, and using responsible rearing protocols, etc. Maybe you were doing it to contribute to a citizen science program, which is a good thing. And, being responsible, you tested each adult before releasing, of them turns out to be infected with OE. Now what? This scenario plays out over and over out there in the world of monarch aficionados and nature lovers. I know fellow monarch researcher Sonia Altizer gets asked this question a lot - she is a leading expert on OE, and the project leader of MonarchHealth - the citizen science program where volunteers sample adult monarchs for OE. The question she gets asked most is what to do with the infected monarch - release it or euthanize it?

Her answer is written on the project website (link here). Basically, she argues that it depends on whether the infection was acquired naturally, or in captivity. If the monarch was collected as a 4th or 5th instar larva, on wild milkweed, and if the rearing procedures were clean (but the monarch still emerged infected), then that means the monarch likely acquired the infection "naturally," and therefore it should be released to nature. Alternatively, if the larva was collected at an early stage, or even as an egg, then the infection likely resulted from contamination of the rearing equipment, or the containers, where other infected monarchs had emerged and that might not have been cleaned carefully. In that case, the OE infection was acquired "unnaturally," and the monarch should be euthanized. So essentially, the answer seems to depend on whether the person suspects the infection to be natural or unnatural.

Full disclosure - I have always disagreed with this answer. I think our different answers to this question also reflect two overall schools of thought on this same issue.

Here's my take: I say, euthanize the infected monarch(s) you raised. Period. No questions asked, and no debate. Recall that this is for monarchs raised in captivity, not necessarily for those captured as adults in the wild. Here's why I say this: First, it is a simple directive, with no way of getting it wrong or misinterpreting it. Second, and more importantly, the overall monarch population simply cannot afford to become more infected than it is. We're already losing tens of millions of monarchs each fall from this infection, and it's pretty clear that this rise in prevalence is not natural (i.e. it is because of us humans). For the home-rearer, allowing one more infected monarch into the world, even if it was naturally-acquired, will not help this situation, either at the local or national scale. That infected monarch could go on to mate and lay hundreds of eggs, each of which will become infected, and so on... I think you can see my stance here.

Here's the interesting thing. She's right. But I'm right too. Her answer really is the correct one in theory. Keep in mind that OE is a natural parasite that has probably been with monarchs and other Danaid butterflies for millennia, and it has probably coevolved with these butterflies. In other words, if a monarch became infected with this natural parasite, then it was destined to be, and we shouldn't tamper with that. But also recall that this answer depends on the person being able to answer a lot of questions about that monarch's upbringing, and in the end, making a judgement call. I think that's asking a lot of people, and, I suspect that many folks just lead with their hearts anyway, and so they probably let the (infected) monarch go if it "looks OK". So while her answer is technically the correct one, I don't think that this approach is working to reduce national OE levels. Or at least, it is time for a different answer.

OK, so of course I'm biased, but my solution is right too, or at least more realistic. With my solution, there is no judgement call, and, the monarch population would be better for it. Of course, we won't be wiping out the OE parasite, even if everyone did this. This parasite will still linger. Keep in mind that it has always lingered in the background, with less than 2% of monarchs ever being infected in the main North American population.

Let me also bring up the issue of what to do in places where OE infections are already really high, like in Florida, or southern California, or perhaps the southern Gulf coast states, like Louisiana, or Mississippi. For people who insist on rearing monarchs in these regions (though in California it is illegal anyway), they will run into this issue over and over, since most larvae are already infected. Some people try to go to great lengths to rear healthy monarchs, using bleach, ultra-clean methods, or whatever, but they really aren't helping as much as they think. Even releasing healthy monarchs in these places only leads to more infections - see a prior blog about this.

For people who live in areas of high prevalence, or even people who live elsewhere, an even better solution to this issue is to simply not rear monarchs in captivity. That way, you will never have to make a judgement call. In other words, leave the monarchs in your yard alone - leave the eggs and leave the caterpillars to nature. Sure, most will be eaten, but that is what is supposed to happen. Monarch eggs and caterpillars are nature's tasty treats. Most will be eaten and will serve to pass on their nutrients and energy to the next bug, which will itself be eaten, and so on. A few will make it to adulthood, and these will likely be better equipped to survive, migrate, and reproduce as adults.

Well, now that I've muddied the waters completely on this issue, I think my work is done!

That's all for now.


Direct link to this blog entry:




The science of monarch butterflies

A blog about monarchs, written by a monarch scientist, for people who love monarchs

bottom of page