by When I was seven years old, my parents drove from Boston to Florida with me in the back seat. We were heading to see my grandparents. It was a lovely family visit. I saw the space shuttle launch, and got to see The Wizard of Oz for the first time. But those are all different stories. Because what stuck with me more than anything else from that trip was how different, amazing, and sometimes frightfully bizarre the natural world could be when you’re far from home. The trip was full of the smell of pine forests, the feel the sea biscuits on my hand, and sights of unfamiliar birds. It was certainly more than I expected, even as a kid already fascinated by the outdoor world. One episode that stuck with my was during a picnic. Decades later, I don’t remember any of the other details, except for the creature that arrived unexpectedly: the monkey slug.
I loved animals. I read up on creatures from everywhere. The stranger and more unfamiliar, the more interested I was in hearing about them or looking at their pictures. And typically, I was never afraid, no matter how strange the creature might be.
But there, creeping across the pavement was a thing I could not have imagined. It was a caterpillar. – Maybe. – But it had… arms? Was that even possible? It moved with a wholly unnatural gait. (At least to my 7-year-old mind.) It jerked and reared. Although it was probably less than an inch long it seemed to move too fast and uncontrolled. And it was heading in my direction! None of my family members had any idea what the thing was. My interest verged on fear, but I certainly didn’t want any one to harm it. I just wanted it to be not-near-me. And I wanted to know what it was, because not knowing how to even place this thing in the universe of my imagination was perhaps the most unnerving part. Eventually, we left. And because this was 1983, and I was seven, there was no way for me to get an answer to this mystery.
Well, it turns out I became a biologist, and one who works with insects. Over the years, I had mostly forgotten that picnic in Florida and the strange and disturbing creature. Until a colleague this summer sent me pictures of a caterpillar she found in her yard in Maine, and suddenly it all made sense.
It was a monkey slug. Now this has to be one of the weirdest names for an insect out there. But if you’ve seen them, it’s fitting. Most caterpillars have three pairs of relatively robust legs at the front and a number of “prolegs” farther back on their abdomen. While they typically move by undulating, they use those legs and prolegs to grip and they have “walk” in their own way. But caterpillars in the family Limacodidae have reduced prolegs that function as suckers. Some even produce a liquid silk to slide along. Hence their common name: slug caterpillars. Many slug caterpillars are much flatter than your prototypical round caterpillar. They can also be very furry, and some species use the hairs as an irritant to repel would-be predators. Like all caterpillars they grow and eventually undergo metamorphosis, molting into a pupa or chrysalis, and then emerging as a moth or butterfly. Slug caterpillars become particularly furry moths. Personally, I find them kind of cute.
The monkey slug caterpillar has evolved long arm-like projections of its furry body. The hairs of the monkey slug Phobetron pithecium don’t seem to irritate humans. While they can occasionally resemble spiders, it’s not certain why they have such an eccentric appearance. Monkey slugs are widely dispersed across the eastern United States, from Maine to Florida and west to the plains. They’re harmless to humans and crop plants, but they tend to live on many plants people enjoy, like apples trees, oak, birch, hickory and dogwood.
I think my 7-year-old self missed an opportunity to get to know this creature better. But the awe I felt then is still with me today. And rather than fear, I can smile at that the amazing existence of such a strange creature.
Video by Cathy Bevier. – And special thanks to Cathy for sharing her backyard discovery of the monkey slug, and reminding me of my own encounter!
Check out The Caterpillar Lab for some excellent videos of monkey slugs.
For more information on the monkey slug and other caterpillars: Wagner, David L. (2010). Caterpillars of Eastern North America. Princeton University Press. p. 44. ISBN 978-1400834143.
