Spring 2003 Volume 12, Number 1
EASTERN TENT CATERPILLAR
by Clifford S. Sadof, Department of Entomology Purdue University
Each spring crabapples and other flowering fruit trees throughout Indiana can be
defoliated by the Eastern tent caterpillar,
Malocosoma americanum. They are called tent caterpillars because they produce
webs in the central crotches of trees (Fig. 1).These caterpillars are an early
season pest, and begin feeding on leaves just as the leaves begin to break bud.
Caterpillars are dark in color with a white stripe on their back and can grow up
to 2' long (Fig. 2).
This insect has some peculiar habits that make it relatively easy to control. Adult moths lay egg masses in late May and June on twigs (Fig.3). Caterpillars hatching from these eggs will crawl toward the center of the tree until they find a branch joint where they start to form webs (Fig.4). Caterpillars remain in webs during the day to avoid predation from birds. At night, caterpillars crawl from the mass of webs to feed on leaves.
If you can reach the webs you can remove the caterpillars that spend their days inside them. Caterpillars can be killed by dropping them in a bucket of soapy water, or by simply squeezing them in your hands. Do not burn nests. While the snap, crackle, pop of burning caterpillars maybe gratifying, burning nests will kill tree limbs.
When many nests are present, or too hard to reach, insecticide sprays can kill caterpillars and reduce defoliation. Two biological pesticides, Spinosad (Fertilome Borer, Bagworm, Leafminer and Tent Caterpillar Spray, or Garden's Alive Bull-Eye), and Bacillus Thuringiensis (Dipel, Thuricide and others) can kill caterpillars. Both these materials are easy on the beneficial insects and bees that keep other insects like spider mites from becoming problems. Although carbaryl (Sevin) or permethrin (Eight) can kill caterpillars they also can kill bees and other beneficial insects.
While their damage rarely if ever affects tree health, the presence of thousands of 2 inch long caterpillars has given more than one homeowner a terrific fright. .Moreover, like most other caterpillars, when they finish growing, they stop eating and begin to search around for a safe place where they can make their cocoons and transform into a night flying moth.
If you are unlucky enough to have this wiggly extravaganza coincide with the annual family barbecue you can use a hard stream of water to hose and corral the caterpillars into a heap that can be shoveled into a bucket of soapy water. To prevent the offensive odor associated with the decay of large numbers of cater-pillars, homeowners should be sure to sweep up the dead insects and toss them into the compost or a trash bin.