Forest Tent Caterpillar – Malacosoma Disstria


Sugar maple, birch, oak, aspen and other deciduous.



Shiny brown egg masses are present from July until early spring of the following year. They differ from those of eastern tent caterpillar in having square edges, and they completely encircle the twigs of host trees. Larvae, which are present in early spring, have distinctive keyhole-shaped white spots on the middle of the back of each segment. Defoliation of all except larger veins and petioles of the leaf occurs in May and June. The adult moths appear in July.

Life cycle

Insects overwinter in masses of 150-200 eggs. Larvae emerge about the time leaves unfold in the spring and may feed at first on opening buds. Later they consume whole leaves. Unlike the eastern tent, forest tent caterpillars do not construct tents. They spin mats on which they rest and make pathways of silken threads to feeding sites. Pupation takes place in white, silken cocoons, often within rolled leaves. Adults emerge in July, mate, and lay eggs.



Loss of woody growth and death of branches may result from heavy or repeated defoliation. Repeated defoliation, along with other stress factors, can kill trees or predispose them to disease or other pests. Bacillus thuringiensis and various chemical insecticides can be used to control larvae. The collapse of large outbreaks which occur periodically have been attributed to depletion of food supplies, unfavorable weather conditions, and natural enemies such as predators, parasites, and pathogens.