Gypsy moth goes through one generation per year. Egg mass hatch typically coincides with budbreak. Gypsy moth spends four to six weeks in the larval stage. The pupal stage of the life cycle lasts approximately two weeks. In the east, adults generally emerge in July.
Adults mate soon after emergence.
Egg masses, which contain 100-1000 eggs, are usually laid almost immediately after mating. The egg mass is the overwintering stage. Early instar gypsy moth damage is characterized by small holes on the interior of leaves. Larger larvae begin feeding at the leaf edges and will ultimately consume the entire leaf except for large veins and the midrib. When the number of larvae on a given tree is high, feeding can result in total defoliation of the tree.