The term “asp” often describes a venomous snake, but in the Southern United States, it refers to a highly toxic insect larva known formally as the puss caterpillar, or the larva of the Southern Flannel Moth (Megalopyge opercularis). This creature is notorious for its deceptive, furry appearance and potent defensive sting. The life cycle of this insect involves a complete metamorphosis, transforming the dangerous, crawling larva into a quiet, harmless adult moth.
The Asp Caterpillar: Appearance and Venom
The asp caterpillar, or puss caterpillar, is an inch-long larva covered in a thick coat of long, silky hairs, resembling a miniature Persian cat or a clump of cotton. Coloration is variable, ranging from grayish-white to golden brown or dark charcoal gray. This soft exterior hides a potent defense mechanism: venomous spines (setae) concealed beneath the outer hairs. The caterpillar’s dense “fur” and teardrop shape obscure its head and legs.
The venomous spines are hollow and connected to a venom gland at the base. When brushed against the skin, these spines break off, embed themselves, and release the toxin. Contact causes immediate, intense, burning pain, often described as similar to a broken bone or a hot coal.
The localized pain can quickly radiate up the affected limb, and the contact site often develops a red, grid-like pattern. Systemic symptoms may follow, including headache, nausea, abdominal distress, or difficulty breathing. These caterpillars are found throughout the Southern United States on trees and shrubs like oak, elm, and wild plum, feeding on leaves.
The Cocoon and Pupation
When the asp caterpillar is fully grown, it stops feeding and begins pupation, transitioning to a non-feeding adult. The caterpillar seeks a sheltered location, often under a leaf, twig, or on the host plant’s bark, to construct its cocoon. This cocoon is a hard, dense structure that provides protection for the transformation occurring inside.
The caterpillar weaves silk and incorporates its own shed larval hairs and spines into the material, creating a fortified, camouflaged shell. The cocoon’s color usually reflects the caterpillar that spun it, often being reddish-brown, gray, or yellow. A distinctive feature is a small, trap-door-like operculum at one end, which the adult moth uses for escape.
The duration of the pupal stage is variable. Caterpillars that pupate late in the season (fall) will overwinter inside the cocoon, remaining dormant until spring. Those that pupate earlier may emerge as adults in just a few weeks, completing metamorphosis.
The Final Form: The Puss Moth
The final form of the asp caterpillar is the adult Southern Flannel Moth, Megalopyge opercularis. This creature possesses none of the danger of its larval stage. The moth is named for its fluffy appearance, with its body and legs covered in long, dense, soft hairs, resembling flannel. Coloration is typically muted (dull orange, cream, or lemon-yellow), helping it blend into its nocturnal environment.
The adult moth’s primary function is reproduction, and it has a relatively short lifespan, often lasting only a few days. The adult Puss Moth is completely harmless to humans because it does not possess the venomous spines. These stinging spines are strictly limited to the caterpillar stage.
The female moth will lay several hundred eggs, usually on host tree leaves, beginning the cycle anew. Adult moths are generally nocturnal and are rarely encountered by people, unlike the highly visible caterpillar.