Urticating hair

Urticating hairs or urticating bristles, i.e. irritating hairs, are one of the primary defense mechanisms used by numerous plants, some New World tarantulas, and various lepidopteran caterpillars. Urtica is Latin for "nettle" (stinging nettles are in the genus Urtica), and hairs that urticate are characteristic of this type of plant, and many other plants in several families. This term also refers to certain types of barbed hairs that cover the dorsal and posterior surface of a tarantula's or caterpillar's abdomen. Many tarantula species eject hairs from their abdomens, directing them toward potential attackers. These hairs can embed themselves in the other animal's skin or eyes, causing physical irritation, usually to great discomfort.