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To rear or not to rear: the Monarch debate

Jason Kay, who gardens in Evanston, Illionois, near Chicago, kindly gave me permission to reprint his  blog about the pro's and cons of raising Monarch caterpillars.

By Jason Kay Garden in a CIty

I am a strong believer in listening to people who know what they are talking about. Unfortunately, sometimes people who usually know what they are talking about shoot themselves in the foot, often by insisting that they know more than they really do.

An example is the current controversy over captive rearing of Monarch butterflies. This is an increasingly popular hobby for many gardeners and others who wish to help restore the population of this beautiful species. The rationale is that 90%+ of Monarch caterpillars do not survive to adulthood (due mainly to predators), but a large majority of those raised indoors do survive so that they can be released as mature butterflies.

Judy and I raised a few Monarchs indoors this year for the first time (fewer than 10), and I can attest that it’s exciting and fun.

But then along came the Xerces Society for Invertebrate Conservation, certainly a worthy organization. However, they published a blog post that was highly critical of captive rearing of Monarchs. This has caused a lot of people to become pretty upset.

Essentially, the post argued that captive rearing was counterproductive because:
-it allows less fit Monarch caterpillars to survive, thus weakening the Monarch gene pool;
-it could lead to a mismatch between the number of Monarchs and available resources (too many Monarchs, too little Milkweed);
-it promotes the spread of parasitic disease due to crowded conditions.

For more detail, go read the whole thing.

A response to the Xerces Society was posted by Chip Taylor, Director of Monarch Watch and Professor of insect ecology at the University of Kansas. Taylor is agnostic on the subject of captive rearing – neither for nor against. In fact, he considers the debate to be an unwelcome distraction.

Taylor argues that the number of captive reared Monarchs released is simply too small to have a significant impact, good or bad, on the overall Monarch population.

What’s more, he says, there is really no data that shows any impact, positive or negative, of releasing captive-reared Monarchs.

The Xerces Society did cite one study that seemed to show a lower survival rate for captive bred Monarchs as opposed to those bred in the wild. However, one of the authors of that study has written that the Society drew unwarranted inferences from his work.

In part, that’s because he was looking at captive bred Monarchs versus wild bred, but captive reared Monarchs are not captive bred. Rather, they are bred in the wild and then brought inside as eggs or caterpillars to be reared.

Beyond that, the issues raised by the Xerces Society are speculative. Certainly, Monarch caterpillars should not be raised in crowded conditions and enclosures need to be cleaned and sanitized – but this is something pointed out in every resource on rearing Monarchs that I have seen.

Taylor argues that habitat loss is the most urgent challenge for Monarch conservation. He cites estimates that one billion additional stalks of Milkweed, mostly in the Upper Midwest, are needed to build a sustainable Monarch population. To read all of Taylor’s post (via Kylee Baumlee’s blog, Our Little Acre), click here.

So apparently, gardeners raising Monarchs at home will not boost the Monarch population in any meaningful way. But there’s no reason to think that it does any harm.

Perhaps the greatest value of rearing Monarchs is not its impact on the butterfly, but its effect on people. Based on our own experience and that of friends, I would say that rearing Monarchs unquestionably creates more Monarch enthusiasts. For Judy and I, it was almost a bonding experience with the species.

More Monarch enthusiasts, I think, means more people willing to dig up more of their lawn and plant more Milkweed and other butterfly-friendly plants. It means more people who will support projects and policies that contribute to Monarch conservation. And that is certainly a positive thing.

Kate's note: I raised Monarchs last year and also found it fascinating. I blogged about it a couple of times

Raising Monarchs, routing aphids

The summer of Monarch abundance

and - after talking to a natural resources ministry official - was left feeling ambivalent. I do consider the practice of buying boxes of butterflies to release at weddings or other events a perverse commercialization. But raising a few rescues is another matter and - as Jason says - increases understanding and appreciation of these wonderful creatures. And that helps us address the critical problem of expanding Monarch habitat. 

Nancy Moysiuk
- 6 November 2018 at 02:52pm

I started by planting milkweed in the yard of my Toronto home. I do not believe that I ever had monarchs reach maturity in the wild. Then I met an entomologist who told me that earwigs consume the immature caterpillars. Sure enough, when inspected, my milkweed plants were riddled with earwigs. While I do attempt to remove the earwigs each year, there seems to be no shortage of them. That was what prompted me to start rearing monarchs. I pick the milkweed leaves with eggs before the earwigs can get them. In a poor year, I might only raise one to adulthood. In a good year, I have come close to 100. My monarchs appear to grow healthy and I have a high success rate for release. It appears to me that where there would have been no monarch maturing from my garden's bounty of milkweed, I am releasing some and that is better odds for their survival. I now have neighbours who notice what I am doing and they are considering growing milkweed as well, which also enhances the opportunity for monarchs to survive. I wonder if the critics of rearing monarchs inside have ever noticed how hard it is for them to survive on their own in a large urban city. ( I can only imagine their struggles in the country due to lack of milkweed plants and pesticide exposure) I disagree with their opinion, at least where Toronto is concerned.
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