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  • Andy Davis

New statement from monarch conservation groups says - For the love of God, stop mass-rearing

Hello everyone,

Today's post is not about a scientific study per se, but about a recently-posted statement that was put out by two well-known conservation groups that relates to the growing hobby of rearing monarchs indoors, and in massive numbers. According to these organizations (and practically every reputable monarch scientist out there, including me), this practice is very, very dangerous to the monarch population, and it needs to stop. In contrast, rearing a few monarchs here and there for teaching purposes, or for citizen science projects is generally acceptable.

The statements were published online by both the monarch Joint Venture, and the Xerces Society, and I'll link to them here:

Xerces decided to expand on this and write a (very well-written) blog about it, which is here -

I would advise you to read these before going further here.

These statements have been released due to a dramatic increase in this practice, where people have taken to rearing hundreds of monarchs in their basements, or kitchens, in an effort to "boost the monarch population". There are now dozens of Facebook groups where this practice is encouraged, and where users typically swap stories about their own rearing operations, and try to one-up each other on how many they rear at a time (usually hundreds, sometimes thousands). These facebook sites only reinforce this practice, and I have noted that not one of the sites is administered by an expert. I do understand that the people doing this have their hearts in the right place, but they are usually unaware of the harm they could be doing to the population. Note that I stressed the word population here - let me come back to that.

Now before giving my two cents on this, let me just say that I am not associated with either MJV or Xerces, but I do agree with this position statement. The statement combines evidence from multiple scientific studies that all show how this practice is very risky, and I'm all about scientific evidence.

Both of the statements outline some of the major issues with mass-rearing, which involve disease spread, weakening of the gene pool, and disrupting the true biology of the species (I purposely oversimplified this last one). I have some thoughts on each of these issues, plus some of my own, below. Forgive me if these seem like ranting, but this practice just has to stop.

First, the issue regarding weakening of the gene pool is something that I might add to here. The Xerces blog post did mention this a little, but it is something that needs to be emphasized because I don't think people have a good handle on what this means. The most common rationale I've heard about captive-rearing, is that in the wild, larval survival is only 5% (or 1%, or a tiny number). But in captivity, survival is 95%. Thus, people use this as evidence that captive-rearing works to "boost the population". There is some logic to this (by simple math alone), however one thing that is almost always missed here is the fact that these 95% were never supposed to live. Have you ever heard of natural selection? Survival of the fittest? There is a reason why monarch females lay hundreds of eggs in the first place. She only needs one to survive to maintain the population - she just needs one larvae to live to adulthood in order to replace herself when she dies. ONE. Out of 400 or so eggs she will lay in her lifetime. That one egg that lives to become an adult butterfly is the one that survived the harsh realities of nature. And it did so because it was the best - the best at eating, dodging predators, avoiding wasps, pupating correctly, etc., etc. This is natural selection, and it is the way mother nature designed this species (and all other insects).

In a captive-rearing scenario, people typically take in all of the eggs they find from the wild, and then rear ALL of them to adulthood - this essentially bypasses natural selection, and it allows monarchs that never would have made it in the real world to survive. In other words, it takes away nature's role in keeping the entire population healthy (there's that word again).

The other point I'll make about the "population-boosting" idea is that I've noticed that a lot of captive-rearing people (rearers) have dramatically ramped up their rearing operations this year, when the summer monarch population is the highest it's been in years. Put another way, it is pretty clear that the monarchs do not need a "population boost" this year, yet these people are determined to give them one! If anything, shouldn't the captive rearing be done when the summer numbers are really low? Not that this practice is condoned, but I'm just saying, the rearers are not being logical with this population boost argument.

Next is the disease issue. When you rear monarchs in close quarters, and/or in large numbers, you run the risk of spreading diseases and parasites among the monarchs. There are many insect diseases, but the one we know the most well is OE. This disease can spread like wildfire in a captive setting. Plus once it spreads, it gets onto all of the supplies and cages you use, so that all subsequent monarchs will be infected too. And most importantly, not all monarchs that get OE infections will die during rearing. In fact, many of these will look and act just like uninfected adult monarchs. Now I know that some monarch-rearers claim that THEIR rearing is done correctly, and that THEIR monarchs are perfectly healthy. Which really means that their reared monarchs flew away - i.e. they didn't die immediately after release. I don't think that this qualifies as a suitable health checkup of those monarchs. In fact, rarely do I ever see a rearing operation where the person routinely checks their monarchs for OE. But what about the other diseases that monarchs get, like viruses, bacteria, etc. Are those monarchs you just released carriers of those? Or more importantly, because you reared them in captivity, in the absence of diseases, did those monarchs develop a healthy immune system that would protect them later in life?

And now for the most important issue in my book - are those captive-reared monarchs you just released at the end of the summer going to die during the fall migration, because they were reared in the absence of natural daylength and temperature? This is a very critical point that was missed by both statements. In recent posts, I've covered the basics of "reproductive diapause", which is the essential physiological condition that monarchs need to be in when they migrate south. This condition seems to be established, or at least triggered, during the larval stage, and the larvae mostly use temperature and daylength as their cues. Essentially, the larvae can tell when it's time to migrate by gauging the environmental conditions of their surroundings, and then that tells them to develop into the migratory (super) generation, which will migrate south. If they do not have these cues, they do not go into diapause. It's that simple. Now, how many rearing operations are done in someone's kitchen, where the temperature is constant, and lighting is artificial? Would monarchs reared like this go into diapause? Probably not. And also, how many people who rear monarchs can tell if their monarchs are in diapause? Any? The point is, that by rearing them in artificial environments, they will not be ready for the migration.

Lastly, there may be some folks out there who don't think this applies to them, because they "don't rear that many." This begs the question, how many is too many? At what point does your kitchen-rearing operation become "mass rearing?" I would say if it's over 100 then it's mass rearing. Please stop.

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The science of monarch butterflies

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

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