Dr. Grow: Eastern tent caterpillars widespread in Midwest

The distinctive residence of the eastern tent caterpillar was found in a tree along Gordonville Road in Cape Girardeau.

I recently received several samples of worms that were found crawling up and down pin oaks and sweetgum trees in the Heartland. An entomologist friend of mine, Larry, identified them as eastern tent caterpillars.

Larry had also been given samples from people whose trees were infested. Because the incidence of these worms was so widespread, we both felt information about this insect would be of interest.

Actually we found caterpillars from two different species, the eastern tent caterpillar and the forest tent caterpillar. They both have a similar life cycle.

The adult eastern tent caterpillar, a moth, lays its eggs in a mass along twigs of trees during midsummer. These eggs over winter and then hatch in early spring. The resulting caterpillars are black, somewhat hairy, and have a yellow stripe down the middle of their back. In contrast, the forest tent caterpillar has a row of keyhole shaped spots down the middle of its back instead of the yellow stripe.

After the caterpillars hatch, they begin forming a tent in the crotch of the host tree. This tent, or web, becomes their home at night and during inclement weather. They leave the web each day to find leaves to eat. the resulting defoliation can be injurious to the host tree.

After a few weeks of feeding, the larvae, now some 2 inches long, congregate on tree trunks and begin to pupate. They then tend to wander off and spin a cocoon in a sheltered place. The adults emerge from the cocoons in midsummer, and the life cycles begins anew.

The favorite host for the eastern tent caterpillar is black cherry. In contrast, the forest tent caterpillar seems to have no favorite host. It has been known to defoliate large forest areas and can cause considerable damage.

If you find these insects in your landscape, don't be alarmed. In most cases very little damage has been done to host trees. If major defoliation does occur, the tree is usually not killed. On the other hand, if defoliation occurs annually for several years, a tree can suffer.

Control is usually very easy. Spray the infested tree with diazanon, malathion, dursbane or cygon. Normally one application is sufficient. Be sure to spray during the day when the caterpillars are out of the tent foraging for food. It is difficult to get an insecticide into the well. When spraying, make sure you always read the label and follow directions.