Megalopyge opercularis is a moth of the family Megalopygidae. It has numerous common names, including southern flannel moth for its adult form, and puss caterpillar, asp, Italian asp, fire caterpillar, woolly slug, opossum bug, puss moth, tree asp, or asp caterpillar.
The inch-long larva is generously coated in long, luxuriant hair-like setae, making it resemble a tiny Persian cat, the characteristic that presumably gave it the name "puss". It is variable in color, from downy grayish white to golden brown to dark charcoal gray. It often has a streak of bright orange running longitudinally. The "fur" on early-stage larvae is sometimes extremely curly, giving them a cottony, puffed-up look. The body tapers to a tail that extends well beyond the body, unlike its relative M. crispata. The middle instar has a more disheveled, "bad-hair-day" appearance, without a distinctive tail. The "fur" of the larva contains venomous spines that cause extremely painful reactions in human skin upon contact. The adult moth is covered in long fur in colors ranging from dull orange to lemon yellow, with hairy legs and fuzzy black feet.
M. opercularis can be found on oak, elm, and wild plum, among others, as well as many garden plants such as roses and ivy. It is distributed throughout the Eastern United States between extreme southeastern Virginia and Florida, the Southern United States, Mexico, and parts of Central America. The caterpillar has 2 broods, one in the summer and the other in the fall. Late larvae may stay in their cocoon all winter, and emerge in late spring as an adult.
