This leaf feeding pest is a particular concern in areas where Dutch Elm Disease is present, because defoliation renders an elm very susceptible to attack by the bark beetles that spread the fungus causing the disease. Healthy trees will usually produce a new crop of leaves by mid-July. After three or more consecutive years of heavy attack, tree growth is slowed and branches in the crown may die back. Cankerworm larvae are light green to brownish-green, often with a darker stripe down the back. They are sometimes called inch worms or loopers.
Cankerworms drop to the ground and burrow into the soil when full grown.
Fall cankerworm moths emerge from their cocoons in mid-September and October. Spring cankerworm moths remain burrowed throughout the summer, fall and winter and emerge as moths from the end of March to mid-May. Wingless female moths crawl up the trees to lay small irregular clusters of fifty or more eggs in bark crevices in the crown of the host tree. The eggs of both the fall and the spring cankerworm hatch in spring. Banding F emale cankerworm moths are wingless and must crawl up the tree to lay their eggs.