Late season caterpillars are out in full force. Many use camouflage or secretive behavior to avoid predators. In contrast, stinging caterpillars have brittle, hollow spines connected to venom glands. These spines easily penetrate and break off in the skin. Then, the irritating venom goes to work.
Reactions to the chemicals vary from slight irritation to pustules, inflammation, and intense pain. Contact usually comes when a person accidentally brushes against a caterpillar that they did not see.