Caterpillars, the larvae of butterflies and moths, come in many shapes and sizes. Though most are harmless, the stinging caterpillars let you know they don't like to be touched.
Stinging caterpillars share a common defensive strategy to dissuade predators. All have urticating setae, whic are barbed spines or hairs. Each hollow setae funnels poison from a special glandular cell. The spines stick in your finger, then break away from the caterpillar's body and spill the toxins onto your skin.
What happens if you touch a stinging caterpillar? It hurts. The reaction depends on the caterpillar, the severity of the contact, and the person's own immune system. You'll feel some stinging, itching, or burning. You might get a rash, or even some nasty pustules or lesions. In some cases, the area will swell or become numb, or you'll get nauseated and vomit.
Stinging caterpillars mean business. Here are some nice, safe pictures to view, so you know what they look like.