The caterpillar of the puss moth, Megalopyge opercularis, also commonly known as the asp caterpillar, is one of the most toxic caterpillars in North America. It is endemic to the southwestern United States and Central America, where it is common, and often found on shade trees such as oaks, elms, maple and citrus, or on small bushes. The 2.5-4 cm long caterpillar is covered with silky yellow, grey, red, or mixed color hairs (setae). Although the caterpillar’s appearance is soft and almost like a small furry cat (possibly inspiring its common name, puss caterpillar) its thick setae hide ridges of short, hollow spines connected to poison glands. When touched, these spines penetrate the skin, injecting poison which causes intense pain, nausea, vomiting, headache and sometimes respiratory distress and stings may require medical attention. Recent molts may also cause a sting. Instead of the usual five prolegs of most caterpillars, those within the flannel moth family (Megalopygidae) have seven. The adult moth, called the Southern flannel moth, is also unusually fuzzy in appearance, with and orange thorax and orange at the base of its blunt yellow wings, a 2.5-4 cm wingspan, and little black furry feet.

(Lyon; Eagleman 2008; Hyche 1998; Wikipedia 2011)