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]