Hag Moth Caterpillar (Monkey Slug) Identification Guide
Recognize this bizarre, hairy-armed caterpillar that mimics a bit of curled dead leaf or spider debris more than a typical larva.
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Key Visual Features
The hag moth caterpillar, commonly nicknamed the "monkey slug," is one of the strangest-looking caterpillars in North America, and it is unlikely to be confused with any other larva once its shape is known.
- Body shape: Small, flattened, and roughly oval, but covered with several pairs of long, curling, fringed lobes ("arms") of unequal length that project outward and curl like tentacles or a fringe of hair.
- Color: Ranges from light tan or golden brown to dark brown, often mottled, resembling a curled dead leaf fragment or bit of debris.
- Texture: The lobes are covered in fine hair-like bristles, giving the whole caterpillar a fuzzy, unkempt appearance.
- Size: Small, usually under an inch (roughly 1.5-2 cm) long.
- Symmetry: The lobes are arranged in pairs down each side but vary in length, giving an asymmetrical, tousled look rather than the tidy rows of spines seen in related slug caterpillars.
Where and When You'll See It
Hag moth caterpillars are found across the eastern United States on a wide range of trees and shrubs, including oak, hickory, dogwood, apple, and persimmon. Look for them on leaves, especially the undersides, from late summer into early fall. Because they resemble bits of dried leaf or debris, they are often overlooked entirely.
Similar-Looking Caterpillars
- Spiny oak-slug caterpillar: Has short, stiff, branching spine clusters rather than long, curling, fringed lobes.
- Stinging rose caterpillar: Brightly striped and tufted rather than lobed and leaf-like.
- Puss caterpillar (southern flannel moth larva): Also fuzzy and unusual-looking, but has a dense, uniform coat of long silky hair covering a teardrop-shaped body, without the distinct curling arm-like lobes of the hag moth caterpillar.
- Dead leaf fragments or debris: The hag moth caterpillar's best camouflage is simply looking like non-living plant matter, so careful observation is often needed to notice it is an animal at all.
Quick ID Checklist
- Small, flattened body with several pairs of long, curling, fringed lobes of unequal length
- Tan to brown, mottled coloring resembling dried leaf debris
- Fine hair-like bristles covering the lobes
- Asymmetrical, tousled silhouette unlike any other common caterpillar
- Found on oak, hickory, dogwood, or persimmon leaves in late summer/fall
Frequently asked questions
Why is it called the monkey slug?
Its curling, fringed lobes resemble tufts of fur or a monkey's limbs, and like other members of the slug caterpillar family it moves with a smooth, gliding gait.
How is the hag moth caterpillar different from other slug caterpillars?
Most slug caterpillars have short, symmetrical spine clusters, while the hag moth caterpillar has long, curling, unevenly sized lobes that give it a shaggy, asymmetrical look.
What does the adult hag moth look like?
The adult is a fuzzy brown moth with wings that can resemble dried leaves, continuing the caterpillar's leaf-mimicking theme.
Where on a plant is the hag moth caterpillar usually found?
It is typically found resting on leaf surfaces, often the underside, where its coloring and shape help it blend in with debris.
Hag Moth Caterpillar (Monkey Slug) identified by the community
Recent Hag Moth Caterpillar (Monkey Slug) finds identified with Bug Identifier.
