If you hear the phrase “monkey slug”, your first thought is probably not of a caterpillar. But that is indeed the common name for Phobetron pithecium, a caterpillar/moth in the family Limacodidae.

Limacodidae are collectively known as the slug caterpillars due to their reduced legs and slimy looking underbelly. They even crawl by means of a liquified silk trail that they glide effortlessly across. So that is where the “slug” part of the name comes from. But “monkey”? No one is quite sure. The adults are called hag moths, which doesn’t sound very flattering, though they are adorable little moths.

I have never seen one of these caterpillars in the wild, however a friend of mine (Sam Jaffe of The Caterpillar Lab) was kind enough to part with a few of his fuzzy little charges. I have no use for them in my research, but they have been fun pets.

A few more facts:
They can cause allergic reactions in some people (I have not tested myself yet, but just look at those hairs and spines!). However they have glided across my hands with no reaction, so it would probably require rubbing the hairs into your skin.
They do have a head, but it is usually hidden.
They feed on a variety of trees and shrubs, mine are feeding on oak.
The “arms” can come off, the hairs are in fact embedded in a scaffold of some sort of slime that covers the body. This is a feature common to many limacodids.

Here are some photos I took of these guys today.