As the larvae grow they begin to feed on leaves. As populations increase, it is not uncommon for trees and forests to be defoliated. The caterpillars mature in the first part of June, with adult moths appearing during the last part of the month, when egg laying takes place. There is one generation per year. Forest tent caterpillars have denuded forests in many areas for up to five years in a row.
Trees can usually survive such defoliation, but with reduced growth.
Disease, other insects, nutrition, moisture and general poor condition may cause tree mortality in defoliated trees. Higher defoliating populations of forest tent caterpillars typically drop after two years due to natural conditions and diseases. Freezing weather shortly after eggs hatch kills large numbers of caterpillars, and excessively high temperatures later in the spring kills large numbers of adults and reduces the viability of newly laid eggs. Egg masses on branches of small trees around the home can be removed and destroyed before hatching. All controls are most effective when applied as soon as all eggs have hatched.