browntail moth, common name for a moth, Nygmia phaeorrhoea, of the tussock moth family. It is a serious pest of forest and shade trees, especially oak. It was introduced from Europe about the same time as the related gypsy moth in the late 19th cent. Browntail moth adults are white, with a tuft of brownish hairs at the tip of the abdomen; the abdomen of the male is rust colored. The female, with a wingspread of 11/2 in. (3.8 cm) is slightly larger than the male. The dark, red- and white-mottled larvae, or caterpillars, may completely defoliate trees. They have nettling hairs that cause a skin rash if touched. Young larvae overwinter in small clumps of leaves fastened together with silk, emerging in early spring. In early summer they pupate in a cocoon in the soil, and the nocturnal adult emerges in about three weeks. An introduced fungus has helped keep this pest in check, and it has not spread in North America beyond New England. However, it is still a serious pest in parts of Eurasia. Good pruning of overwintering leaf nests and spraying are important control measures. The browntail moth is classified in the phylum Arthropoda, class Insecta, order Lepidoptera, family Liparidae.