Milkweed Tussock Moth Caterpillar

Euchaetes egle, the Milkweed Tussock Caterpillar or Milkweed Tiger Moth, is a moth in the family Arctiidae. It is a common mid- through late-summer feeder on milkweeds and dogbane. Like most species in this family, it has chemical defenses it acquires from its host plants, in this case, cardiac glycosides (Weller et al., 1999). These are retained in adults and deter bats, and presumably other predators, from feeding on them (Hristov and Conner 2005). Only very high cardiac glycoside concentrations deterred bats, however (Hristov and Conner 2005). Adults indicate their unpalatability with clicks from their tymbal organs (Simmons and Conner 1996).
(Description courtesy of Wikipedia)