Hag Moth Caterpillar (Monkey Slug)

The hag moth caterpillar, widely nicknamed the monkey slug for its bizarre resemblance to a tiny, hairy primate, is among the most unusual-looking larvae found in North American woodlands. Rather than a recognizable caterpillar shape, it presents as an irregular clump of curled, fuzzy, brown to tan projections that can easily be mistaken for a bit of windblown fur, dead leaf debris, or even a shed tarantula skin.

This strange appearance is a form of disguise, helping the caterpillar go unnoticed by predators and casual observers alike as it rests on bark or leaves, blending remarkably well with its surroundings.

• Body is small, brown to tan, and covered in dense, curling hair-like projections of varying lengths
• Several pairs of these fleshy, hair-covered arm-like lobes curl outward and can appear asymmetrical from individual to individual
• Overall silhouette resembles a tuft of fur, a spider, or debris rather than a typical caterpillar
• True body segments and legs are obscured beneath the hairy projections
• Fine stinging hairs are present among the curled projections
• Unmistakable once recognized due to its unique shaggy, asymmetric shape unlike any other North American caterpillar

This species is found across much of the eastern United States, from the Gulf Coast north into New England and west into the Midwest, in deciduous forests, woodland edges, and shrubby yards. Caterpillars are present from summer into fall, resting and feeding on a variety of hardwood and shrub leaves.

The caterpillar feeds on the leaves of a wide range of trees and shrubs, including oak, cherry, dogwood, and many others, and is a generalist among slug caterpillars. Its unusual, fur-like appearance functions as camouflage and mimicry, helping it avoid detection by blending in with debris or resembling a small spider rather than an edible caterpillar. The curled projections carry fine hairs that can sting in defense if the caterpillar is touched, adding to its disguise-based strategy against predators.

Females lay flat, translucent eggs in small groups on host leaves. Larvae hatch and develop through several instars over the summer, gradually forming their characteristic curled, hairy projections as they mature. The caterpillar spins a small, tough, brown cocoon, often attached to bark or leaf litter, within which it overwinters. It emerges as an adult hag moth the following season, typically producing one generation per year across most of its range.