Description

The eastern tent caterpillar, Malacosoma americanum, belongs to the family Lasiocampidae. The larvae are hairy and possess a solid white stripe down the upper (dorsal) midline of the body, black and white stripes down the back and a row of oval blue spots on the sides. The larvae live communally in large, irregular tents of silk attached to tree branches. As larvae feed, they increase the size of the web until it is a foot or more in length. Mature caterpillars can reach up to 2 to 2.5 inches (5.0-6.5 cm) long. Eastern tent caterpillars feed on wild cherries, apples and crabapples and may be found on hawthorn, maple, cherry, peach, pear and plum trees as well. Adult moths are yellow or tan with thick, short, furry bodies. The forewings have two darker oblique lines near the middle. The wingspan is about 1.5 inches (3 cm). Eastern tent caterpillars can be confused with fall web worms (Hyphantria cunea) because they both create tents. Fall web worms produce silk nests at the ends of branches and feed inside the nest, while eastern tent caterpillars make tents in forks of branches or tree trunks and then leave the nest to feed. Further, eastern tent caterpillars are active during the spring, and fall web worms occur later in the season, from mid-summer through early fall.

Eastern tent caterpillar, Robert L. Anderson, USDA Forest Service, Bugwood.org.

Life Cycle

Eastern tent caterpillars have one generation per year. Eggs overwinter within an egg mass on branches of host plants. They are covered with a hard, shellac-like substance (spumaline). The larvae hatch during March and congregate in forks or crotches of host plants and construct their tents. As the larvae feed, the size of the web increases. The larvae feed away from the tent during the day and shelter within the tent at night. After six to eight weeks, larva pupate, and adult moths emerge from cocoons about three weeks later, typically during May.

Egg mass, Robert L. Anderson, USDA Forest Service, Bugwood.org.

Tent, Pennsylvania Department of Conservation and Natural Resources — Forestry, Bugwood.org.

Adult, Lacy L. Hyche, Auburn University, Bugwood.org.

Seasonality and Control

Control is generally not necessary. Populations tend to fluctuate, with outbreaks occurring every several years. Large infestations of caterpillars can result in defoliation of trees. Damage to plants often looks worse than it actually is. Many trees are able to generate a new flush of foliage following defoliation, and variations in population densities mean many trees are not defoliated annually. The single generation annually means plants do not suffer from repeated waves of defoliation throughout the growing season. The feeding activities of larvae perform a valuable ecological service by recycling a portion of tree biomass back to the soil via their abundant droppings. These provide nutrients that promote herbaceous growth and improve overall floral diversity in forest and urban park ecosystems. The large silken nests in trees and large numbers of wandering caterpillars crawling over plants, walkways, and roads can be aesthetically unpleasant. If desired, early suppression of the eastern tent caterpillar can be effective. Larvae within the tents are protected and difficult to kill with insecticides. Natural predators, parasitoids and diseases help in reducing eastern tent caterpillar numbers. These include several braconid, ichneumonid and chalcid wasps. Effective insecticides may be found in the Insect Pest Management Guide in the chapter titled Ornamentals and Flowering Plants. This publication is available on our website: www.lsuagcenter.com.