The vast majority of lepidopteron (moths and butterflies) caterpillars, even many with hairs, do not present a threat. However, there are some with hairs that are modified for defense. These are collectively called urticating hairs from the Latin urtica meaning "nettle." Indeed, the hairs on stinging nettle (Urtica dioica), which are called trichomes; provide a good model for the venom injecting mechanism used by some of the more serious urticating hairs found on caterpillars.

Click Here For More