The eggs overwinter and begin hatching in April and May the following year. Older caterpillars are distinctive with a dark body and four pairs of raised blue spots and six pairs of raised red spots along the top of the body. Tufts of brown hair project from the sides. Caterpillars feed from May through late June or early July, then seek sheltered places to pupate. Adult moths begin emerging in July.
Males are smaller than the heavier-bodied females.
They are strong fliers. Females have white wings with dark wavy lines and a wingspan of about 2 inches. After mating, each female produces a single egg mass containing up to 1,000 eggs and then dies. The gypsy moth has a broad host range and feeds on over 300 species of trees and shrubs. When population densities are high, caterpillars will feed on almost any vegetation, although they usually continue to avoid ash, sycamore, black walnut, catalpa, mulberry, redcedar, and arborvitae.