Eastern Tent Caterpillars

The eastern tent caterpillar, Malacosoma americanum, is a common defoliator of many ornamental and fruit trees during the early spring.

The insect overwinters as eggs, which are laid in mass on small twigs approximately a pencil width in diameter. Egg masses are about ½ inch long, black in color and encircle the twigs on which they are deposited. These masses can contain several hundred eggs.

Eastern Tent Caterpillar Life Cycle

Eggs hatch in early spring as leaf buds begin to open. The young caterpillars gather in the forks of the limbs where they construct their dense, silken tents. These caterpillars do not feed within their tent but congregate there during the night and in inclement weather. They move out of tents to feed upon the newly opened leaves, and in the process, may completely defoliate branches within 3 feet of the tent.

As the caterpillars grow, their tents enlarge. Larvae become full grown in four to six weeks, at which time they are about 2 inches long. Larvae then wander away individually from the tent in search of protected areas to form a cocoon. Adult moths typically emerge from cocoons in June and July. There is only one generation per year.

Eastern Tent Caterpillar Description

Eastern tent caterpillar larvae are covered with long, soft hairs and are bluish-black in color with a white line running down the back. Moths are reddish-brown in color with two pale lines running across the forewings.

The webbing produced by eastern tent caterpillar can often be confused with those produced by fall webworm. Unlike the eastern tent caterpillar, fall webworm forms loose silken webs around foliage at the ends of branches. Additionally, fall webworm activity generally occurs later in the season.

Eastern Tent Caterpillar Damage

The preferred hosts of eastern tent caterpillar are black cherry, crabapple and apple trees. Damage can range from light to heavy defoliation, depending on the size of the tree attacked and the number of tents present. The webbing produced in trees can also be aesthetically displeasing.

Eastern Tent Caterpillar Control

For mature, well-established trees, controls are seldom necessary; however, if caterpillars attack young trees, or for aesthetic preservation, the tents and associated larvae can be removed and destroyed. Burning the tents out of trees is not recommended, because this can easily damage the tree or spark a wildfire. The bacterial insecticide, Bt ( Bacillus thuringiensis), as well as many synthetic insecticides are also effective against eastern tent caterpillar. During the winter, egg masses can be pruned out and destroyed to prevent tents from developing the following spring.

Eastern tent caterpillar egg cases, larvae and adult (Photo credit: D. Frank).

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