Could Raising Captive Monarchs Mess Up Migration?

A late-season male Monarch butterfly nectars on my New York Asters

As you may have heard, alarming new research about raising Monarch butterflies was published recently, by Ayşe Tenger-Trolander, Wei Lu, Michelle Noyes, and Marcus R. Kronforst. Their study found that indoor-reared fifth-generation Monarch butterflies did not display southward flight in tests, which means they wouldn't migrate properly. Uh-oh!

I haven't been able to access the entire article yet, just the abstract linked above, and a write-up in Science. But even those limited sources give me concern about my techniques in raising Monarchs. The researchers raised both commercially-bred monarch caterpillars and wild-caught. Although they used the caterpillar generation that's supposed to migrate, both groups  had neither the elongated wings of migratory individuals, nor showed predominantly southward flight under test conditions. (They attached the mature butterflies to poles in the experiment, so they could observe which directions each butterfly would head. Previous research has shown that in these conditions, migratory monarchs reliably try to fly southward.) The scientists even raised some wild individuals outdoors until the point of pupation, and found that if those individuals eclosed indoors, they too seemed to have lost the tendency to migrate!

Two of my Monarch chrysalids last year, raised indoors & then released after eclosing.

Not unexpectedly, this has thrown the butterfly-raising community into a bit of a tither. Are we actually exacerbating the threats to monarch migration as we try to help? When our efforts include raising the caterpillars indoors, especially the migratory generation, it looks like maybe so.

From what I'm seeing on various email groups, Twitter, and Facebook, many caterpillar hobbyists and citizen scientists are distraught. Should we change our habits and maybe abandon the hobby of raising monarchs?

Honestly, I've already been somewhat concerned about my butterfly raising. This isn't the first study to indicate we might be doing more harm than good, for one thing. I had thought, though, that the main problem was using captive-bred caterpillars, like classrooms might when they mail-order caterpillars from who knows where in order to have them on time for the lesson plan. Since I only raise wild-caught individuals (whether starting as egg or already-hatched caterpillar), I hoped I wasn't doing too much damage.

But another effect of captive-raising caterpillars can be to allow weak genes to survive and get passed along. Since I'm protecting the caterpillars from natural stresses, a trait that would have made an individual less likely to survive isn't actually a problem, and may end up expressed in the next generation too. Especially if I raise every monarch caterpillar I can find, I might still be making my local population less fit. Now this new research just adds more support to reconsidering my actions.

This Monarch caterpillar lived its entire life outdoors at Brookside Gardens, where I found it getting ready to pupate.

I can't speak to what anybody else will or should do, of course, but here are ways I'm planning to change my caterpillar husbandry:

• In general, I will collect and rear no more than 50% of the eggs and/or caterpillars that I find in my garden, of each species. The rest I'll leave wild and unbothered, to fend for themselves. (This also means I'm not reducing the amount of available food for hungry birds!)
• For monarchs in particular, I will rear no more than two caterpillars per generation for the first four generations each year.
• Once the migratory generation's eggs are laid, starting around August in my area, I won't raise any monarchs. 

I also considered trying to create an outdoor setup for raising monarch caterpillars, rather than keeping them in my office indoors. That will take quite a bit more planning, however, so stay tuned.

Another idea was to raise monarchs indoors until they look ready to pupate. Then I could move them outside while they pupate and later eclose. Although I'm not sure exactly what the pupa get from being outdoors, the new research does indicate it's a crucial factor in triggering migration: "In fact, merely eclosing indoors after an otherwise complete lifecycle outdoors was enough to disrupt southern orientation."

I'm not changing how I raise Black Swallowtail caterpillars, or other non-migratory species, as much as I'm changing my treatment of monarchs. I'm definitely reducing how many I raise, going by the 50% rule above. Also, if I find a single egg or caterpillar on any day, I won't bring that in at all. I know I still might be changing something essential in these butterflies by raising them in the protected environment of my office. However, I do call them "pets" sometimes because I know they may not be the same as totally wild individuals. I guess they're kind of half-wild; I do release them as soon as they eclose. I always hope they make my local population larger, going on to mate and lay more eggs that lead to more caterpillars. This summer I'll keep thinking about whether I feel comfortable bringing them inside any more.

As much as I love watching the caterpillars up close, am I being selfish by bringing them inside?

Do you raise butterflies indoors, or have you ever? What do you think about this new research? I'd love to hear your thoughts, whether you plan to stop raising butterflies at all or keep on caring for them like you always have.  Perhaps you even have a totally different method of raising caterpillars than I do. Whatever the case, please leave a comment below to keep the conversation going!

Monarch Caterpillars at Last!

This summer has been a very sparse one for caterpillars in my yard so far. I’ve found not a single Black Swallowtail egg or caterpillar, nor seen any adult butterflies. As I mentioned in this post about my Promethea Moth, I had only one overwintering Black Swallowtail chrysalis this spring, which eclosed shortly after its cage had blown away during a storm. By the time I found the cage again, the trapped butterfly (and its companion Spicebush Swallowtail) had died for lack of food. Poor things.

I hoped that the wild population did better than my captives, but I haven’t seen any signs of that yet. I’m letting dill volunteers sprout all over my garden, though, just in case there are a few wild Black Swallowtails nearby.

That being said, though, my caterpillar hobby didn’t go bust this summer after all. Over the last few weeks, my yard’s milkweed patch was finally discovered by Monarch butterflies! I have both swamp milkweed (Asclepias incarnata) and common milkweed (Asclepias syriaca). My husband spotted a Monarch paying special attention to the swamp milkweed while I was at work one day. When I checked those plants, I found my first monarch egg… and two plump caterpillars! Clearly there had been monarchs visiting my yard before that day too.

One of the first big happy caterpillars

The egg hatched just a few days later. I actually didn’t find the caterpillar the day it hatched—I forgot to check the cage that night. The next day, though, I discovered the tiny hatchling had wandered off its milkweed leaf onto the side of the cage. I quickly coaxed it onto a scrap of a milkweed leaf, and pinned that onto a fresh sprig of milkweed.

So tiny: how much smaller the hatchling is compared to the pin shaft!

Although I nearly had a heart attack when I realized the hatchling had gone without food for an unknown time, not staying on the milkweed probably saved it from being eaten by its ravenous companions. The two older caterpillars were now eating everything in sight, so I decided to keep two separate cages: one for eggs and hatchlings, and one for third-instar and older caterpillars.

Eggs and babies on the right, late-instar caterpillars on the left.

Over the next several days, I kept finding more eggs and caterpillars each time I went out to the milkweed patch. At first they were all on swamp milkweed, but eventually I found eggs on common milkweed as well. It seemed like every time I looked outside there was another monarch ovipositing! Eventually I gave up on collecting all of the eggs, as I was running out of room. I figure I’ll let the eggs hatch in the wild and then bring in caterpillars as I find them, so by then. As of this writing I have 21 caterpillars from tiny hatchlings to fat fourth-instars,  four more hanging in J, and four chrysalids. Whew!

A wild "j" that I found at Brookside Gardens a few years ago

The first two Monarch chrysalids

This sudden population explosion is actually pretty typical in my area. The monarch numbers have been silently building through the summer, culminating in the fourth and final generation, the migrators. (I think these caterpillars are the last generation, anyway.)

So far, it seems that Monarch caterpillars develop much faster than Black Swallowtails, especially transitioning from last instar to pupa. The two first caterpillars went from spinning their silk button to hanging in “j” (equivalent to how Black Swallowtails hang in their safety belts) to a glistening green chrysalis in about 24 hours! I didn’t get a photo of either caterpillar in j because of that, the speed really caught me by surprise. Black Swallowtails, on the other hand, usually spent a day or two in prepupa after spinning their safety belt, before finally molting into chrysalis. I don’t know how long the Monarchs spend in chrysalis yet, but as soon as the first two eclose I’ll be able to update this post.