Eastern tent caterpillars build a tent or web in the fork of a tree. The real damage, however, is the defoliation caused by these chewing insects. The damage is done by the larval stage, the caterpillar. Depending on the size of the population, an infestation of Eastern tent caterpillars is capable of totally defoliating a tree. The caterpillars feed away from the tent during the day, but return to it for protection on rainy days and at night.

The Eastern tent caterpillar overwinters in an egg mass which has been deposited around a small twig. Each mass is about ½ inch long, oval-shaped, shiny, and brown to gray. It contains as many as 300 eggs. As the leaves on the host tree appear in early spring, the eggs hatch and the newly emerged larvae begin spinning protective silken tents in the twig crotches. Colonies of 200 to 300 caterpillars rest in these tents at night or on cloudy, rainy days and emerge on sunny days to feed on tender young leaves. A fully grown Eastern tent caterpillar can reach 2 1/2 inches long. It has a hairy body and dark coloring, with showy white stripes running lengthwise down its back, bordered by pale blue spots.

By the end of May, the caterpillars leave the tree to form cocoons on tree trunks, fence posts and other hard structures. They spin white, silken threads into a 1 inch cocoon that encloses a dark brown pupa. The insect will remain in the pupal stage for approximately two weeks. By late June, adults will emerge. The adults are dark, chocolate-brown moths, with two white stripes running obliquely across the forewings. After emerging, they mate and lay their eggs on twigs of the host plant. These eggs will not hatch until the following spring.

Cultural management:

Remove and destroy the tents when they are first noticed. It is best to remove them at night or on cloudy days when caterpillars are inside the nest.

Chemical management:

If needed, chemicals should be applied as soon as the tents are evident since the insect is more susceptible when young. Bacillus thuringiensis var. kurstaki is a low toxicity product that can be sprayed when the caterpillars are young (mature caterpillars may not be killed by Btk). The product needs to be ingested, so it should be sprayed on the foliage, not on the larvae or the tent.

The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.

For more information, contact The Morton Arboretum Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).