Hair of the Caterpillar

By Rory Boothe

Published May 1, 2026 at 7:21 AM EDT

The saddleback caterpillar (Acharia stimulea) is the larva of a Limacodid moth. Its venomous spines deliver what may be the most potent sting of any caterpillar in North America. Large eye spots on its back end (shown in this photo) add further deterence to predators. The caterpillar is green with a brown saddle-shaped spot on its back, a black face with two yellow eye-like spots. Spine-like bristles protrude from appendages and skirt the body. — The saddleback caterpillar (Acharia stimulea) is the larva of a Limacodid moth. Its venomous spines deliver what may be the most potent sting of any caterpillar in North America. Large eye spots on its back end (shown in this photo) add further deterence to predators.

I'm a gardener thus caterpillars are my enemy. I can‘t keep the armyworms out of my beans, and a pack of hornworms is eating up my tomatoes.

And what about their hair? It‘s enough to give me hives.

Most caterpillars are covered in hair-like bristles called setae (SEE-tee). These tiny filaments are often too pale to see. But a number of caterpillars are covered in thick swathes of setae that they mean for us to see and to heed.

The caterpillars in my garden are covered in setae that can cause some mild skin irritation for people with sensitive skin. Setae act like caterpillar adhesives that have detachable ends that can lodge in the skin of an unlucky handler. The small ends can also float into mucus membranes, like in our eyes, and prove almost impossible to extract.

The Puss Caterpillar

Color camouflage and setae allow the hornworms in your garden to blend in seamlessly with tomato stalks. Other disguised caterpillars are truly dangerous, with hollow bristles connected to venom sacs. A few stinging caterpillars live in the U.S.

One of those is covered in a dense wooly coat that makes it resemble a Persian cat, garnering it the name the puss caterpillar. Beneath the puss caterpillar‘s wooly fur are many short venomous spines; for an unsuspecting trespasser these spines deliver a sting, causing radiating pain that‘s often more severe than other caterpillar stings.

But to be at least a little fair to caterpillars, for the most part you should be aware of them, not anxious about your encounters with them. Most hairy caterpillars are harmless and beautiful to behold, intent only to eat their way to metamorphosis, and through my garden.

Thank you to Stanton Gill of the University of Maryland and Montgomery College for reviewing this episode's script.

Sources And Further Reading:

Greenmind Guides. 17 Furry Caterpillar Types: An Identification Guide. Owlcation: Stem Entomology Guides. September 28, 2018. Accessed on November 1, 2018.

Greendmind Guides. Caterpillar Types and Identification Guide. Owlcation: Stem Entomology Guides. August 26, 2018. Accessed on November 1, 2018.

Malaque, Ceila M.S. Andrade, LÚCIA. Madalosso, Geraldine. Tomy, Sandra. Tavares, FLÁVIO L. Seguro, Antonio C. A CASE OF HEMOLYSIS RESULTING FROM CONTACT WITH A LONOMIA CATERPILLAR IN SOUTHERN BRAZIL. The American Journal of Tropical Medicine and Hygiene, Volume 74, Issue 5, May 2006, p. 807 - 809 DOI: https://doi.org/10.4269/ajtmh.2006.74.807

"Urticating hair." Wikipedia. Accessed November 1, 2018.