NC State Extension Publications

Description and Biology

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Puss caterpillars, Megalopyge opercularis, are also called asp caterpillars because of their potent stings. They are called puss caterpillars because their thick, fluffy setae resemble the fur of a pussycat. Adults are called flannel moths because of their fluffy, wavy, flannel-like scales. The moths evidently lay their eggs in batches because young larvae sometimes feed in groups on the surface of the leaf. Older larvae devour entire leaves. Two generations occur each year with peaks of abundance of caterpillars in July and October. Second generation caterpillars finally spin a dense cocoon on the host plant in which they spend the winter. The cocoon usually has a noticeable bump on the back and on the front there is usually a distinct, round hatch cover (the operculum) through which the moth emerges in the spring (the scientific name opercularis was named for the distinctive operculum.).

The puss caterpillar looks harmless, but stings painfully

The puss caterpillar seems to covered in fur.

Puss caterpillar with operculum to the left

The puss caterpillar spins a brown, tough, silk cocoon that weathers to gray.

Top view of puss moth

The puss caterpillar moth is also called a flannel moth.

Host Plants

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Puss caterpillars feed on various deciduous trees and shrubs, especially elm, hackberry, maple, oak, and sycamore. Puss caterpillars are usually not abundant enough to be noticed although rare outbreaks have been widespread causing severe defoliation. On humans, they produce a very painful sting when brushed against (brushing against the caterpillar breaks tiny hollow spines filled with an urticating fluid that produces a painful stinging sensation. The pain may last several hours. Swelling associated with the sting may be evident for several days). Other symptoms aside from pain, stinging, and swelling are nausea, headache, fever, itching, abdominal distress, chest pain, difficulty breathing, numbness, vision problems. Other than that, the sting is not troublesome.

Residential Recommendation

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Puss caterpillars are usually not abundant enough to be noticed although rare outbreaks may be widespread and may cause severe defoliation. Sevin or one of the Bacillus thuringiensis pesticides should give adequate control although Bt is not very effective on older caterpillars.


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This Factsheet has not been peer reviewed.


Professor Emeritus
Entomology and Plant Pathology

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Publication date: June 27, 2013
Revised: May 8, 2023

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