Eastern Tent Caterpillar

Malacosoma americanum

The adult moth is reddish-brown with two whitish stripes running obliquely across each forewing. Full grown caterpillars are generally black and about two inches long. They have a white stripe down the back and a series of very blue spots between longitudinal yellowish lines. The larvae are quite hairy.

Eastern Tent Caterpillar Adult
Figure 2. Eastern Tent
Caterpillar Adult

Life History
The insect overwinters in the egg stage in a distinctive mass attached to the smaller twigs of the host plant. These masses may be as large as 3/4 inch long and contain 150-350 eggs. They usually have a varnished appearance. Its favorite hosts include wild cherry, apple, and crabapple but will feed on ash, birch, black gum, red gum, willow, witch-hazel, maple, oak, poplar, peach, and plum. In the spring, when new leaves begin to unfold, the young larvae begin to build webs in a branch fork or crotch. From these webs, the larva go forth to feed on the new foliage. When populations are high, complete defoliation of the tree may occur. After feeding, the larvae migrate to off-host objects such as fences, tree trunks or other natural or man-made objects, where they spin silken cocoons. Adults usually emerge in late June and early July, mate and eggs are laid on twigs. There is one generation each year.

Severe defoliation by the eastern tent caterpillar may occur for several consecutive years. When populations are high, trees can be completely defoliated putting the tree in a stressed condition. Fruit trees will bear little or no fruit while ornamental plants can be weakened leaving them susceptible to secondary agents such as borers and cankers. Aesthetically, the webs can be quite unsightly and a general nuisance.

Eastern Tent Caterpillar Egg Mass on Twig
Figure 4. Eastern Tent
Caterpillar Egg Mass on Twig

Nonchemical Control
Eastern tent caterpillars can be controlled quite effectively by removing webs either by tearing them out or pruning them out. Removal of overwintering egg masses before spring will also help reduce natural populations. Various parasites also aid in naturally reducing populations.

Chemical Control
Tent caterpillars can be controlled by applying insecticidal sprays as soon as the larvae are noticed.