Identifying and Controlling Eastern Tent Caterpillars

Eastern tent caterpillars, Malacosoma americanum, build unsightly silk tents in cherry, apple, and other landscape trees during early spring. The caterpillars feed on leaves of these host trees and may cause significant defoliation if present in large numbers. They can also be a nuisance as they tend to wander when they're ready to pupate, making themselves at home on houses and decks.

Make Sure You've Really Got Tent Caterpillars

First, be sure what you have are eastern tent caterpillars and not another similar pest. Eastern tent caterpillars appear in early spring and build their tents in the crotches of tree branches. As their name suggests, fall webworms also build tents but theirs are located at the ends of branches, forming an envelope around the foliage. Some people confuse eastern tent caterpillars with gypsy moth larvae but gypsy moths do not construct tents and they usually appear a little later in spring than tent caterpillars.

Prevention and Manual Controls for Tent Caterpillars

If you have a few caterpillar tents in an apple or cherry tree, don't panic. Eastern tent caterpillars rarely infest ornamental trees in large enough numbers to kill landscape plants. Because they appear in early spring and complete their life cycle by summer, most of your host trees will have time to produce more leaves after initial defoliation. Pest control may not be necessary at all, however, if the infestation is overwhelming—or you just can't stand the sight of caterpillar tents in your trees—there are some things you can do to deter the invasion.

To prevent tent caterpillars, the best defense can be a good offense. In the autumn, after the leaves have fallen, scout the branches of host trees for egg masses. Prune out any you find, or scrape them from the branches and destroy them.

If you do find yourself facing an invasion, knowing your enemy can be the best way to rid yourself of them. Tent caterpillars rest inside their tents after they feed so you can actually remove them manually. When you notice a large group of caterpillars in the tent, use a stick or gloved hands to pull the tent from the branches, caterpillars and all. For a large tent, try winding the silk around a stick as you pull it from the tree. To eliminate the caterpillars, simply crush them or drop them in a pan of soapy water. In the past, people often set fire to caterpillar tents. However, since the practice does more harm to the tree than the caterpillars do, it is not recommended.

Biological and Chemical Controls for Tent Caterpillars

Young larvae may be treated with Bacillus thuringiensis var kurstaki, or Bt, which is applied to the foliage of infested trees. Bt is a naturally occurring form of bacteria that interferes with the caterpillars' ability to digest food. After the caterpillars ingest Bt, they stop eating immediately and die within a few days. You do not need to spray the tents or the caterpillars. Late-stage caterpillars, especially those that are already migrating to pupate, cannot be treated effectively with Bt.

Some contact or ingestion pesticides work on eastern tent caterpillars as well. If you feel the infestation is sufficient to require this drastic an intervention, contact a pest control specialist in your area to ensure the safety of pets and wildlife.