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Before I go on to post today’s short piece, here’s an update on the Monarch caterpillars along with a bit of musing over their social behaviour.

Above is a typical scene that plays out here each morning. I take each tray of caterpillars out to the yard, remove them, toss out all of the old leaves, wash the tray, then fill it with fresh leaves. While I’m cleaning and refilling the container, I leave the caterpillars to wander around for a couple of minutes. It’s quite interesting to see how they behave when placed close together on a few leaves. Normally, Monarchs are not really “social” caterpillars. Yesterday, I watched a female Monarch butterfly ovipositing on Milkweed plants, leaving perhaps two eggs on different leaves of each plant before moving to another. In nature, I doubt that more than two or three caterpillars would ever inhabit one plant at the same time. In fact, having seen how quickly they are eaten by predators, I always feel pretty lucky when I find two caterpillars on a single plant.

When you put a group of Monarch caterpillars together (such as I do each day), their interaction seems to indicate that, unlike some other species, they aren’t particularly sociable. In fact, some of them become quite grumpy if another moves into their personal space. Yesterday, I made a couple of little movie clips of some of these reactions that certain individuals had when approached by their tray-mates. This is one of the shorter clips (about 800kb). The format is .mp4, which I believe should play on most media players. There is no sound on the clip.

The other thing that I’ve noticed is how much these caterpillars use their antennae to touch things, including each other. Of course, when they do reach out and touch a fellow tray-mate, it often provokes a grumpy reaction. This is a longer clip (about 1.7mb) showing both touchy-feely behaviour, and a couple of rebuffs. So much for the image of a peaceful Monarch caterpillar quietly munching on a leaf. Seems that too much togetherness can make them feel grumpy too. By the way, in this clip, I find the behaviour of the larger caterpillar quite interesting. It seems to like to use its antennae to sweep the leaf ahead of it, but watch how it occasionally turns and touches the caterpillar to the left. The smaller caterpillar looks as though it’s giving the larger one a “get away!” gesture a couple of times. After the second rebuff, the larger caterpillar appears to become much more tentative and holds its antennae a little away from the smaller caterpillar.

Now for the updates — here’s how things stand as of this morning. There are about 50 caterpillars at various stages of development from “just hatched” through to starting-to-pupate. There are 2 caterpillars hanging upside-down from silk, so they will probably be chrysalises by tonight. There are 3 chrysalises. And one butterfly has eclosed and been released. More as it happens.

Tags: Monarch caterpillars, Danaus plexippus, caterpillar behavior