1996, Schmidt 1999, 2000), along with differences in the leg and body measurements, the disposition of eyes and scopulae, coloration (Simon 1892; Pocock 1903; Mello-Leitao 1923; Schiapelli & Gerschman de Pikelin 1979; Raven 1985; Smith 1995; Prentice 1997), the type of urticating setae (Cooke et al.
Urticating setae (barbed spines on the caterpillar's processes) are a defense mechanism that cause burning and irritation, sometimes severe, when touched.
The most painful experience, though -- and the only time I was ever hurt by an animal -- was when I was stung by a poisonous caterpillar with urticating spines in the Amazon.
Also caterpillars represent a public health hazard because they have thousands of hairs which contain an urticating, allergenic or irritating protein called thaumetopoein.
Novak, "Thaumetopoein: an urticating protein from the hairs and integument of the pine processionary caterpillar (Thaumetopoea pityocampa Schiff., Lepidoptera, Thaumetopoeideae), " Toxicon, vol.