The Collaborative International Dictionary of English v.0.48:

Io moth \I"o moth`\ (?; 115). (Zool.)
   A large and handsome American moth (Hyperchiria Io), having
   a large, bright-colored spot on each hind wing, resembling
   the spots on the tail of a peacock. The larva is covered with
   prickly hairs, which sting like nettles.
   [1913 Webster]

WordNet (r) 3.0 (2006):

io moth
    n 1: large yellow American moth having a large eyelike spot on
         each hind wing; the larvae have stinging spines [syn: io
         moth, Automeris io]