Megalopyge opercularis

(J.E. Smith, 1797)

southern flannel moth, puss caterpillar, asp, Italian asp, fire caterpillar, woolly slug, opossum bug, puss moth, tree asp, asp caterpillar

Species Guides

Megalopyge opercularis bissesa(Southern Flannel Moth)

Megalopyge opercularis is a in the Megalopygidae, notable for its highly venomous larval stage and strikingly different form. The caterpillar, known as the puss caterpillar, is densely covered in hair-like setae that conceal venomous spines capable of delivering extremely painful stings. The adult, called the southern flannel moth, is covered in soft fur ranging from dull orange to lemon yellow. The has two annually in much of its range, with late-season larvae sometimes in cocoons.

Megalopyge opercularis bissesa by no rights reserved, uploaded by Sinaloa Silvestre. Used under a CC0 license.

Megalopyge opercularis bissesa by (c) Sue Carnahan, some rights reserved (CC BY), uploaded by Sue Carnahan. Used under a CC-BY license.

Pronunciation

How to pronounce Megalopyge opercularis: /ˌmɛɡəˈlɒpɪdʒi oʊˈpɜːrkjələrɪs/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

The puss caterpillar is distinguished from similar Megalopyge by its tail that extends well beyond the body, unlike M. crispata which lacks this distinctive tail. Among stinging caterpillars, it is uniquely recognized by its dense, soft, fur-like appearance concealing venomous spines—resembling a small mammal rather than a typical caterpillar. The southern flannel is identified by its compact, heavily furred body and small wings relative to body size. Color variation in larvae is extensive, making size and tail structure more reliable than coloration alone.

Images

Habitat

Found in wooded areas, forests, and suburban landscapes; larvae feed on foliage of various trees and shrubs including oak, elm, wild plum, apple, birch, hickory, pecan, persimmon, and rose; also occurs on garden plants such as roses and ivy.

Distribution

Eastern United States from extreme southeastern Virginia south to Florida; throughout the Southern United States; Mexico; parts of Central America; parts of South America.

Seasonality

Two annually: one in summer and one in fall; late-season larvae may remain in cocoons throughout winter, emerging as in late spring; adult activity peaks in spring and summer depending on geographic location.

Diet

Larvae feed on leaves of various woody plants including oak, elm, wild plum, apple, birch, hickory, pecan, persimmon, and rose; also reported on garden plants such as roses and ivy.

Host Associations

Quercus spp. - larval food plantoak
Ulmus spp. - larval food plantelm
Prunus americana - larval food plantwild plum
Malus spp. - larval food plantapple
Betula spp. - larval food plantbirch
Carya spp. - larval food planthickory
Carya illinoinensis - larval food plantpecan
Diospyros virginiana - larval food plantpersimmon
Rosa spp. - larval food plantrose
Hedera spp. - larval food plantivy

Life Cycle

Complete with four stages: , larva, pupa, . Larva passes through multiple instars; early instars have curly, cottony appearance, middle instars develop disheveled look without distinctive tail, final instar has pronounced tail extension. occurs in cocoon with hair pockets and . Two per year in most of range; late fall larvae may in cocoons over winter, emerging as adults the following spring.

Behavior

Larvae are slow-moving and feed solitarily on foliage; the dense hair-like setae serve as defensive concealment for venomous spines beneath. are and attracted to light. The caterpillar's appearance of a small, furry mammal is a form of protective mimicry that may deter some .

Ecological Role

Herbivore as larva, consuming foliage of various trees and shrubs; serves as prey for various and despite defenses; may contribute to pollination though specific role is not well documented.

Human Relevance

The puss caterpillar is considered one of the most venomous caterpillars in North America. Contact with the concealed spines causes immediate, severe pain described as comparable to broken bones or blunt-force trauma, with including burning, swelling, nausea, headache, abdominal distress, rashes, blisters, and in severe cases chest pain, numbness, or difficulty breathing. The condition is termed erucism or urticarial dermatitis; M. opercularis is the most commonly reported source of caterpillar stings in the United States. Medical attention is recommended for reactions. First aid involves removing embedded spines with cellophane tape; various remedies including ice packs, antihistamines, and topical treatments have been reported with varying success.

Similar Taxa

Megalopyge crispataSimilar appearance and venomous spines; distinguished by lack of tail extension beyond body in M. crispata versus pronounced tail in M. opercularis
Norape ovinaWhite flannel moth caterpillar with similar dense hair-like setae and venomous spines; distinguished by different coloration and plant preferences including black locust
Automeris ioIo moth caterpillar with prominent venomous spines; distinguished by clusters of branched spines radiating from body segments rather than dense fur-like covering
Hemileuca spp.Buck moth caterpillars with venomous spines; distinguished by prominent branched spines and preference for oak foliage without dense fur-like concealment
Phobetron pitheciumHag moth or monkey slug caterpillar with unusual fleshy appendages; distinguished by bizarre lateral lobes rather than uniform furry covering

More Details

Venom mechanism

The urticating spines are hollow, barbed structures that break off upon contact and embed in skin, delivering venom through a gland at the spine base. The venom composition includes multiple bioactive compounds contributing to intense pain and inflammatory response.

Defensive mimicry

The caterpillar's resemblance to a small mammal (Persian cat) represents protective mimicry that may reduce by visual , while the concealed spines provide active chemical defense against tactile predators.

Parasitoid associations

The ichneumon Calliephialtes grapholithae has been reared from M. opercularis; this wasp typically attacks concealed and the caterpillar's cocoon likely provides such concealment.