While working on the front yard, we ran across this odd creature at the base of a rogue Hackberry seedling. It seemed fairly obvious that it was some sort of caterpillar, until we saw it move. Then it was like… WHOA. Instead of seeing it move along like a regular caterpillar with its legs and prolegs (though apparently a caterpillar actually moves by its gut), what was visible on this caterpillar was a wavelike motion as it traveled. The closest creature I could compare it to, barring that of something from the ocean, was a slug. Turns out that I was right on the money… its common name is actually “slug caterpillar,” or in this case a Spiny Oak Slug Caterpillar. I’m fairly confident about the ID, except that there seems to be a wide variation in color for these little guys. If I were to guess, their coloration might have something to do with what actually tree they are feeding on, or what instar they might be in, but again, just a guess.
To share this amazing undulating movement, we took a video, seen below. We used a macro to get in close to see the waves, hence the occasional moments when the caterpillar goes out of focus. But the gist of the movement is there.
Since this is the first time I’ve ever run across this type of caterpillar, I don’t have a lot of details about it. It will turn into a moth, and my instincts NOT to touch it were spot on. Like other slug caterpillars in the family, it has a painful sting, though this one is milder than some of its cousins. Also, its thoracic legs are reduced, contributing to those rolling waves being such a predominant feature.
Among its host plants, the Spiny Oak Slug Caterpillar eats the leaves of Oak (no big surprise there), Hackberry (also no surprise), Ash, Cherry, Willow, and many other trees. Though we yanked out the Hackberry seedling — it was growing right in the middle of a multi-trunked Yaupon — we took the caterpillar over to another Hackberry being allowed to grow.
Finding things you didn’t know existed is so fun!