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  • Andy Davis

What everyone needs to know about rearing monarchs - from a science standpoint

OK, here it is - the first real post about perhaps the most controversial subject in the realm of monarchs, and one that is sure to generate lots of comments (I even upgraded my website to handle the anticipated onslaught).

So I just read the latest news story about a couple of guys in Iowa who are mass-rearing monarchs by the hundreds and thousands - see the story here - in an "attempt to save the monarchs". This is probably the 3rd or 4th story I've seen this year of people doing this. In fact, I bet a lot of people reading this blog have a couple hundred monarchs in plastic tubs in their house right now. In fact in the last decade there has been a real surge in this activity, and this year, people are taking it to an extreme. I saw one story of a woman who quit her job to rear her monarchs! The basic idea people have in their heads is that monarchs are declining, so we must therefore try to increase their numbers. And, when people realize that less than 10% of monarch larvae survive in the wild, they quickly bring the eggs and larvae inside to "protect them from predators". Somehow, this practice of rearing monarchs has become so commonplace (i.e. everyone's doing it), and so ingrained into the psyche of monarch folks that no one has ever stopped to ask if this is safe. And, I know for a fact that this activity has never been rigorously tested by science, which is what I'll discuss in this week's post.

If you're reading this you may be thinking, how can this be bad for monarchs? We're increasing their numbers, and that must be good! Well, yes and no. You are releasing more monarchs into the wild than there would have been if you had not brought them inside, BUT (this is a big but), you have no way of knowing if those monarchs you released are just as fit as wild monarchs. You may see them fly away, and perhaps even hang around your garden for a while, but what you don't know is anything about their internal physiology. For example, do you know if those reared monarchs have a competent immune system? Or does their metabolism match that of wild monarchs, which is important for the migration? More importantly, do they have any latent, 'subclinical' infections or disease, that aren't obvious? From a scientific standpoint (the gist of this post), very few of these questions have been rigorously tested, and I know the published monarch literature very well.

Even though there is little concrete data on this, there is good reason to believe that reared monarchs are not as fit as wild ones. For starters, rearing essentially bypasses natural selection in the wild. Monarchs lay gazillions of eggs (well, hundreds, anyway) for a reason - the eggs and larvae get picked off by predators, they get sick, and what have you. But that is a natural part of the cycle of life and it is designed to ensure only the fittest genetic individuals make it to adulthood. In other words, they aren't all supposed to survive. That's the way mother nature intended it to be, and that's why they lay so many eggs. By bringing the eggs all in and 'protecting' them, it ensures that ALL of them do survive, even the runts and genetically inferior ones. How many times have we seen photos of wierd-looking caterpillars someone raised? Those ones would have been removed from the population in the wild, by predators, just as it's supposed to be. By sidestepping natural selection in the wild, rearing may well end up watering down the gene pool.

Pretty much the only piece of hard evidence we have so far on rearing monarchs comes from the recent paper by Gayle Steffy, which I wrote about in a previous blog, and it does not paint a pretty picture of reared monarchs. Gayle's data showed reared monarchs had an absolutely terrible migration success rate, which could be because they were smaller, or emerged later than they would have in the wild, or maybe again it was something about their physiology that made them ineffective migrants. Still another possibility is that maybe most of them died shortly after they were released! We don't really know, but either way this evidence does not support the premise that rearing monarchs boosts the population.

So let's talk about the disease issue next. For folks who have been rearing monarchs forever, they know that diseases can get into your colony, or stock, or whatever you call it (my wife hates the word stock - it makes them seem like commodities). And, those experienced people probably think that as long as you segregate 'sick-looking' monarchs, and euthanize monarchs with OE (if they are responsible enough to test for it), then the rest of their reared monarchs are healthy. Not true. Just because it flies away does not mean it doesn't have hidden parasites, viruses or other nasties, just waiting to be spread throughout the local population.

Then, what about the rearing operations where OE is not tested for (gasp)? Keep in mind that monarchs with this parasite do not always look sick, in fact they often look perfectly healthy on the outside (see the monarch parasites website). But, those normal-looking monarchs are actually carrying millions (yes, millions - we've counted) of OE spores, which are designed to fall off the monarch when they fly, lay eggs, mate, etc. They also can contaminate an entire rearing room, including all tubs, bins, and tools that they came in contact with. If that happens, then all other monarchs in the colony get infected. So if you're one of the few people that do test for OE, good for you. But how many people are there out there that don't? One in five? I cringe whenever I hear about a person rearing hundreds of monarchs and releasing them into the wild without testing. If by chance some of those untested monarchs were sick with OE, that means that not only did those reared monarchs not help the local population, they probably also contaminated every milkweed in sight for miles. And the crazy thing is, OE is just one of the butterfly diseases we happen to know about.

So now let me turn to the current scientific opinion on rearing, and it's also not good. I can say with confidence that of the monarch scientists I know (this includes Lincoln Brower), most of them are not supportive of mass monarch rearing, because of the many unanswered questions around it, and the huge potential for introducing and spreading diseases among wild monarchs. This is evident in the recent Monarch Joint Venture statement about responsible rearing, and in another scientific position statement about purchasing mass-reared monarchs from commercial breeders.

I'm winding down here and I know I've thrown a lot of information out there in this post, so let me summarize the big points here:

- The physiology of reared monarchs is unknown, and has not yet been thoroughly studied by science

- Mass rearing bypasses natural selection, watering down the gene pool

- Most monarch scientists do not support mass rearing

- There is clear evidence showing reared monarchs are less fit than wild ones in the migratory generation

- Mass rearing has tremenous potential of spreading hidden diseases and is therefore very dangerous

Let me finish by saying that I am not against rearing a dozen or so monarchs in-home for educational purposes, or to inspire people to conserve, and all that jazz. What I'm against is MASS-REARING, which is what leads to real problems. At what point does it go from the former to the latter? I'd say when your operation is in the triple digits, then it's mass-rearing.

That's it for now. All comments on this topic are welcome, but let's try to keep the focus of the comments on the science, which is what this posting (and this website) is all about.

The science of monarch butterflies

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

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