Megalopyge

Larvae are distinguished from other hairy caterpillars by the extreme density of long, hair-like setae that completely obscure the body form, combined with concealed venomous spines—unlike tussock moths (Erebidae: Lymantriinae) which have prominent tussocks of hair but different spine arrangement, or slug caterpillars (Limacodidae) which have reduced legs and a flattened, slug-like form. Adults are recognized by their stout, furry bodies and reduced wing venation lacking a discal cell in the forewing. The family Megalopygidae is distinguished from related Zygaenoidea families by the combination of flannel-like scaling, reduced mouthparts, and distinctive larval morphology.

Larvae occur in diverse terrestrial habitats including deciduous forests, woodlands, forest edges, and tallgrass prairie remnants. They feed on foliage of broadleaf trees and shrubs. Adults are typically nocturnal and attracted to light. Specific microhabitat preferences vary by species, with some associated with oak-hickory forests and others found in prairie-forest transition zones.

The genus is distributed throughout the Americas, from the eastern United States south through Mexico, Central America, and into South America. Individual species have more restricted ranges: Megalopyge opercularis occurs from Maryland to Florida and west to Texas; M. crispata is found in the central United States including Missouri; other species are restricted to Neotropical regions.

Adult flight periods vary by species and latitude. In temperate regions, adults are active primarily during summer months (June–August). In subtropical and tropical regions, multiple generations may occur with adults present across warmer months. Larvae are typically observed from late spring through early autumn.

Larvae feed on foliage of various woody plants including oaks (Quercus), hickories (Carya), black walnut (Juglans nigra), persimmon (Diospyros virginiana), apple (Malus), birch (Betula), pecan (Carya illinoinensis), and rose (Rosa). Specific host associations vary by species. Adults have reduced, non-functional mouthparts and do not feed.

• Quercus - larval host plantmultiple species
• Carya - larval host plantmockernut hickory and others
• Juglans nigra - larval host plantblack walnut
• Diospyros virginiana - larval host plantpersimmon
• Malus - larval host plantapple
• Betula - larval host plantbirch
• Carya illinoinensis - larval host plantpecan
• Rosa - larval host plantrose

Holometabolous development with four life stages: egg, larva, pupa, adult. Females lay eggs on host plant foliage. Larvae pass through multiple instars, with early instars often appearing as small, white, fluffy clusters. Later instars develop more hair and may show color pattern changes. Pupation occurs within a dense, felted cocoon attached to vegetation or in leaf litter. Number of generations per year varies from one in northern temperate regions to multiple generations in southern and tropical areas.

Larvae are solitary feeders on host plant foliage. When disturbed, they may curl into a defensive ball, concealing the head and exposing the dense hair covering. The urticating spines beneath the hairs serve as a potent chemical defense against predators. Adults are nocturnal and readily attracted to ultraviolet light. Females release pheromones to attract males; males use their plumose antennae to detect these chemical signals.

Larvae function as primary consumers, feeding on woody plant foliage and contributing to nutrient cycling. Their potent chemical defenses make them unpalatable to most vertebrate predators, though some specialized parasitoids and invertebrate predators may exploit them. The ichneumon wasp Calliephialtes grapholithae has been recorded as a parasitoid of Megalopyge opercularis larvae.

Larvae are medically significant due to severe envenomation caused by urticating spines. Contact produces intense burning pain, localized swelling, erythema, and blister formation; systemic reactions including nausea, headache, and lymphadenopathy may occur. Medical attention is recommended for severe reactions or eye contact. Despite this, larvae are sometimes handled inadvertently due to their innocuous, furry appearance—earning common names like 'puss caterpillar' that suggest petting. Adults have no economic importance.

• Limacodidae (slug caterpillar moths)Both families have stinging larvae, but Limacodidae larvae have reduced prolegs and move with a slug-like gliding motion, lacking the dense hair covering of Megalopyge; adults have different wing venation and body form.
• Erebidae: Lymantriinae (tussock moths)Larvae of some tussock moths are hairy and possess urticating hairs, but they display prominent tussock tufts and a more visible body form beneath the hair, unlike the completely obscured body of Megalopyge larvae.
• Norape (white flannel moth genus)Also in family Megalopygidae; larvae are similar in general appearance but typically have different color patterns and hair density; adults show subtle differences in wing shape and pattern.

• venomous
• urticating spines
• medically important
• flannel moth
• puss caterpillar
• defensive hairs
• nocturnal
• light-attracted
• oak feeder
• hickory feeder

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Look but do not touch: puss caterpillar, Megalopyge opercularis; White flannel moth, Norape ovina; Io moth, Automeris io; buck moth Hemileuca spp.; and hag moth, Phobetron pithecium — Bug of the Week
• Megalopygidae | Beetles In The Bush
• Bug Eric: A Potential New Host Record for Calliephialtes grapholithae (Hymenoptera: Ichneumonidae) from a Paper Wasp nest (Hymenoptera: Vespidae: Polistes metricus)
• Bacterial Communities Associated with Megalopyge opercularis (Smith) (Lepidoptera: Megalopygidae): Exploring Poisonous Lepidopterans