This article is about Phobetron pithecium. For Lithacodes fasciola, also known as the ochre-winged hag moth, see Yellow shouldered slug.
"Monkey slug" redirects here. For the other moth with this common name, see Phobetron hipparchia.
Phobetron pithecium, the hag moth, is a moth of the family Limacodidae. Its larva is known as the monkey slug.

Life cycle

There is one generation a year in the north, but two or more in the southern United States.

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Larva, Michigan, mid-August

Underside of larva, showing reduced legs
The larva is distinctive, with no close analogues although it may be mistaken for the shed skin of a hairy spider or leaf debris. It has six pairs of curly projections, three long and three short from the flattened body, each densely covered in hairs. According to David L. Wagner, who experimented on himself, the hairs do not sting, contrary to popular belief. However, susceptibility can vary among humans and it may produce a reaction in some people. Some members of the family Limacodidae do sting. Like all limacodids, the legs are shortened and the prolegs are reduced to suction cups. The "arms" can fall off without harming the caterpillar. Maximum length of larvae, 2.5 cm.

It is solitary and is not a very significant agricultural threat, but it is a common sight in orchards.

Pupates in a cup-shaped coccon with a circular escape hatch.

The adult moth has a wingspan of up to 3 cm. The male has translucent wings, and the female is drab brown and gray, with yellow puffs on her legs. The day-flying female is said to mimic a bee, complete with pollen sacs, and the male mimics a wasp.

Food plants

Eats a variety of deciduous trees and shrubs, not limited to: apple, ash, birch, cherry, chestnut, dogwood, hickory, oak, persimmon, walnut and willow.