Gypsy moth is an introduced pest. Infestations are most frequent in forest strands with abundant oaks and/or gray birch. Apple is also a preferred host. However, gypsy moth feeds readily on a wide range of broad-leaved trees and conifers. Sugarbushes in the vicinity of oak forests, abandoned apple orchards, or sites with abundant gray birch frequently suffer defoliation. This damage occurs early in the growing season when leaves begin to unfold. Severely defoliated trees usually produce a second crop of leaves.

The full-grown caterpillar (Fig. 49) is hairy and 1.5 to 2.5 inches long (35 to 65 mm). The head has yellowish-orange markings. The back has a double row of five pairs of blue spots, followed by a double row of six pairs of red spots. The buff-colored egg masses (Fig. 50) are conspicuous on tree boles and branches, and often are the first indication of a pending gypsy moth infestation.