Bungee-Jumping Inchworms

An inchworm I spotted slowly spooling itself down from a tree last fall

As an arthropod enthusiast, I tend to pick up bugs a lot – specifically caterpillars. There’s nothing quite like the joy of holding a caterpillar.

You have to be careful with inchworms, though. One time I was letting an inchworm crawl around on my hand, and it started bobbing its head around my index finger. I thought this was weird, but he soon started crawling around again and I kind of forgot about it. I set the inchworm down on a leaf and started to walk away, but saw it dangling below my hand again not even a second later – apparently he’d woven a thread into my finger that yanked him off the leaf when I started to leave.

And now I take special care to keep an eye on the inchworms I pick up so they don’t sew themselves to my skin and give themselves whiplash when I think I’ve left them behind.

If you’ve ever encountered an inchworm, it was probably crawling on a tree or dangling from one. After hatching, the inchworm spends its days as most caterpillars would – eating. Then, when it’s time to pupate (usually in the spring or summer), the inchworms descend from the trees on bungee-cord-like threads. If the inchworms pupate during the spring, they’ll become moths within a few weeks, but they’ll stay in their cocoons through the winter if they pupate in the fall.

In its adult form, the inchworm is known as a geometer moth. There are over 35,000 species of geometer moths worldwide, and interestingly, some female geometer moths are incapable of flight – some may even lack wings altogether (here’s a picture). Instead of flying to seek a mate, they wait in the trees for males to find them.

One of the more famous geometer moths is probably the peppered moth. I wouldn’t say that I hold a grudge against the peppered moth or anything, but I’ve had to hear about this guy year after year after year in like, every biology or environment-related class I’ve taken. It’s basically the poster child for the theory of natural selection (aside from Darwin’s finches, of course). I can’t believe I’m reciting this of my own free will, but here’s the gist: before the industrial revolution, peppered moths were mostly “peppered” to blend in with tree bark while the black moths got eaten by birds. Industrial revolution happens, smog turns the trees black, now all the peppery moths are getting eaten and the black moths multiply. The end. Well, not the end, because the trees aren’t so sooty anymore so the peppery moths are multiplying again, but you get the point.

Hear that, public education system? We get it. Please stop telling me about the peppered moths, I promise that information is ingrained in my brain now. Camouflaged moths don’t get eaten by birds and survive to pass on their genes. I get it.

Sheesh, and I thought we learned about the water cycle too much.

Moving on from the peppered moth: if you thought the inchworm got its name for being an inch long, you are surprisingly incorrect. Not only are inchworms actually about a centimeter long (let’s call them centipillars), they actually get their name from the way they seem to be taking measurements as they walk. This funny way of moving is due to the location of the caterpillar’s prolegs (the hind, sticky ones) – while most caterpillars have five sets of prolegs near the middle of their bodies, inchworms have only two or three sets near the end of their bodies, which they pull up to their thoracic legs in an inching manner as they crawl.

Here’s a final fun fact before you go: a defense strategy of the inchworm is being able to stick its body straight out from the branch it’s climbing on to resemble a twig.

And an interesting defense strategy of mine is walking out of class if any of my professors mention peppered moths again. Just kidding… but the temptation is real.

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