Larvae of all Hemileuca species have urticating spines, which means that they emit a chemical that irritates anything that touches the spines, causing an annoying rash or stinging pain depending on the level of contact. The pain can last up to a half hour (personal experience!).
Here are photos of the complete life cycle of the Elegant Buckmoth, Hemileuca eglanterina. The eggs are from a female I found several years ago (she laid them on the inside of the cage zipper!), the rest of the photos are of the group I found last year, ending with the adult male that emerged today.
|Hemileuca eglanterina eggs|