There are three species of white-marked tussock moths, Orgyia detrita, Orgyia leucostigma, and Orgyia definita, found across the eastern United States. Orgyia is Greek for a unit of measurement “the length between outstretched arms.” Their life cycle begins in the winter as eggs, from which caterpillars hatch from April to June. These mature over 30 days and create cocoons. Adults emerge two weeks later and mate; new eggs are laid on the surface of old cocoons by the flightless females.

All three species have similar characteristics, and while their adult form is gray and drab, their larval or caterpillar form is striking. Orgyia leucostigma (illustrated here) has a deep red-colored head and matching red dots (glands) on its back, coupled with clumps of short, vertical yellow hairs (called dorsal tussocks) on the first four abdominal segments, all surrounded by an inviting covering of fluffy long black ‘plume hairs’.

They are most commonly encountered by people in spring and early summer. Symptoms usually begin between 30 minutes and three hours.

They look friendly and fuzzy, especially when they raise the front of their body to search for their next path forward, the “hair pencils” looking like arms reaching out (hence the name Orgyia; see image at right. They are most commonly encountered by people in spring and early summer; however, your reaction of “how cute, I must pick it up” should be tempered by the knowledge that looks can be deceiving. Those hairs and warning colors are a clear announcement that they should be treated with avoidance, not petting, as these structures can cause injury to skin, eyes, and mucous membranes. There are 52 species of moths spanning 10 families of Lepidoptera that are known to have structures that can cause injury to humans—including Orgyia.³

Although they look benign, those attractive hairlike structures covering the caterpillar, especially the tussocks, are specially designed to act as passive armor to protect the caterpillar from predators. They cause injury, and therefore avoidance, among animals intending to eat them—or cause pain and problems in those curious enough to touch them.

The Hairs (Setae)

The brittle tussock hairs from the clumps on the caterpillar’s back (called urticating hairs) have backwards-angled barbs along their length, which, once they have poked into your skin or landed in your eyes, break off and travel deep into your tissues in a linear fashion, resisting withdrawal once imbedded.^1,5