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.