News from Bob's Market & Greenhouses, Inc.

Populations of the eastern tent caterpillar, Malacosoma Americanum, fluctuate from year to year, with outbreaks occurring every several years. Defoliation of trees, building of unsightly silken nests in trees, and wandering caterpillars crawling over plants, walkways, and roads cause this insect to be a pest in the late spring and early summer. Eastern tent caterpillar nests are commonly found on cherry, apple, and crabapple, but may be found on hawthorn, maple, cherry, peach, pear and plum as well.

The eastern tent caterpillar overwinters as an egg, within an egg mass of 150 to 400 eggs (pictured left). These masses are covered with a shiny, black varnish-like material and encircle branches that are about pencil-size or smaller in diameter.The caterpillars hatch about the time the buds begin to open, usually in early March. These insects are social; caterpillars from one egg mass stay together and spin a silken tent in a crotch of a tree. Caterpillars from two or more egg masses may unite to form one large colony. During the heat of the day or rainy weather, the caterpillars remain within the tent. They emerge to feed on leaves in the early morning, evening, or at night when it is not too cold.

The larvae are hairy caterpillars, black with a white stripe down the back, brown and yellow lines along the sides, and a row of oval blue spots on the sides. As the larvae feed on the foliage, they increase the size of the web tent until it is a foot or more in length (right). In 4 to 6 weeks the caterpillars are full grown and 2 to 2-1/2 inches long. At this time, they begin to wander away individually from the nest in search of protected areas to spin a cocoon.

The cocoon is about 1 inch long and made of closely woven white or yellowish silk and is attached to other objects by a few coarser threads.The adult moth emerges from the cocoon about 3 weeks later. The moth is reddish-brown with two pale stripes running diagonally across each forewing. Moths mate and females begin to lay eggs on small branches. The eggs will hatch next spring. There is just one generation per year.

Prevention and early control is important.

Removal and destruction of the egg masses from ornamentals and fruit trees during winter greatly reduces the problem next spring. In the early spring, small tents can be removed and destroyed by hand. Larger tents may be pruned out and destroyed or removed by winding the nest upon the end of a stick. Burning the tents out with a torch is not recommended since this can easily damage the tree.
Young caterpillars can be killed by applying an insecticide containing Bacillus thuringiensis or other insecticides include carbaryl, methoxychlor, and malathion. Larvae within the tents are protected beneath the webbing and are more difficult to kill with an insecticide.