Eastern Tent Caterpillar Fact Sheet

Fact Sheets > Insect Fact Sheets > Eastern Tent Caterpillar

The Eastern Tent Caterpillar, Malacosoma americanum (Fabricius) is reported to have been present in the United States since the 1600's, and is responsible for forming unsightly silk-webbed nests at branch forks. Their population peaks every 8 to 10 years, when large infestations can completely defoliate trees in late spring/early summer.

Plants Attacked

Eastern tent caterpillar's primary host plants are wild cherry (Prunus pensylvanica), apple (Malus) and crabapple (Malus). Occasionally, they feed on deciduous forest and ornamental trees such as ash (Fraxinus), birch (Betula), blackgum (Nyssa sylvatica), willow (Salix), witchhazel (Hamamelis), maple (Acer), oak (Quercus), poplar (Populus), cherry (Prunus), peach (Prunus), and plum (Prunus).

Insect Identification

The eastern tent caterpillar lays a mass of eggs that encircles the twigs of the host plant. The dark brown, oval mass contains between 150 - 350 eggs, and has a varnished appearance. While young larvae are uniformly black in color, later instar caterpillars are hairy and black with white, brown, and yellow stripes and blue spots on their sides. Fully grown larvae are approximately two inches long. The caterpillars pupate inside white cocoons and emerge as reddish brown moths with white stripes on the forewings and a one-and-a-half inch wingspan.

Mature larva with distinct color markings	First instar Eastern tent caterpillar larvae

Life History

Winter	Egg mass overwinters on twigs.
Spring	The larvae hatch when the wild cherry leaves begin to unfold (late April.) The young caterpillars move to a fork in the branch spinning fine strands of silk wherever they crawl. They build a web (tent) and begin feeding on new leaves for six to eight weeks. The web increases in size as the caterpillars feed and grow in size, until the tent is nearly a foot long.
Summer	When the larvae are fully grown, they leave the host tree and find a place to spin cocoons. They pupate inside the cocoons for about three weeks before transforming into reddish-brown moths. Adult emergence occurs in late June or early July. After mating, the females deposit egg masses around small twigs on host plants.
There is one generation a year in Pennsylvania.

Damage Symptoms

Tent located in the tree branch fork

If large populations occur, the caterpillars can severely defoliate a tree, increasing its susceptibility to invasion by secondary insect and disease pests. Damage occurs early in the season when the tree's carbohydrate reserves are at a low level, so control is more critical at that time than when insects defoliate trees later in the summer. Unlike fall webworms, the larvae of the eastern tent caterpillar do not feed within their nests but use them as shelter from inclement weather. The nests can be an eye sore when exposed on a defoliated tree.

Eggmass on a wild cherry twig	ETC spinning cocoon

Management Options

Biological	Eastern tent caterpillar larvae have several natural enemies including other insects, toads and birds. Small beneficial wasps will parasitize the eggs, larvae, and pupae of this pest. Bacillus thuringiensis var. kurstaki (Bt) is effective in controlling early instar caterpillars (less than one inch long).
Mechanical	Pruning and removing of small twigs that hold egg masses, before egg hatch, is an effective way of reducing populations the following year.
Chemical	Registered insecticides should be applied when the caterpillars are first noticed, with sprays directed at the foliage surrounding the tent. It is important to note that the caterpillars leave the tent during the day to feed on foliage and return at night and during rainy weather. Control Measures for Eastern Tent Caterpillar

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Authored by:
Katherine Mazzey, Penn State Extension Program Assistant
Michael Masiuk, Extension Agent, Penn State University - Allegheny County

Sources
Collins, J. (1996). Tent Caterpillars. University of Kentucky College of Agriculture. http://www.uky.edu/Agriculture/Entomology/entfacts/trees/ef424.htm.

Day, E. (2002). Eastern Tent Caterpillar. Virginia Polytechnic Institute & State University. Virginia Cooperative Extension. http://www.ext.vt.edu/pubs/entomology/444-274/444-274.html

Eastern Tent Caterpillar. Michigan State University Extension. http://www.msue.msu.edu/msue/imp/mod02/01500620.html

Eastern Tent Caterpillar. University of Massachusetts Extension's Management Guide for Woody Ornamentals. http://www.umassgreeninfo.org/fact_sheets/defoliators/eastern_tent_catepillar.html

Hoover, G.A. (2000). Woody Ornamental Insect, Mite, and Disease Management. Penn State College of Agricultural Sciences. pp.26, 31, 55. http://woodypestguide.cas.psu.edu/

Hoover, G.A. (2002). Eastern Tent Caterpillar. Department of Entomology. Penn State.

Johnson, W.T. & Lyon, H.H. (1976). Insects That Feed On Trees And Shrubs, pp.168. Comstock Publishing Associates. Cornell University Press.

Shetlar, D. J. (2000). Eastern and Forest Tent Caterpillars and Their Control. Ohio State University Extension Fact Sheet. http://ohioline.osu.edu/hyg-fact/2000/2022.html