The Puss Moth (Cerura vinula) is a lepidoptera from the family Notodontidae. The puss moth is stinging caterpillar, Megalopyge opercularis, commonly called an asp. This is one of the most toxic caterpillars in North America. The mature larva is 1 to 1½ inches long with seven pairs of prolegs (suction-cup like claspers on the rear of the body). This larva of the puss moth shows as it appears when disturbed and ready to sting. Intense, throbbing pain develops almost immediately witnin contact with the caterpillar.