Eastern Tent Caterpillars
by Don Janssen, Extension Educator
The caterpillar colony uses the nest for protection against weather and predators. They venture out of the nest several times a day to feed on tree leaves. As the caterpillars increase in size, they add additional layers of silk to the nest.
Small trees hosting large numbers of caterpillars can easily be defoliated, in which case the caterpillars may move to another tree, make a new nest and continue to feed.
Full-grown eastern tent caterpillars may reach 2 or more inches in length. They hatch as leaves are opening in spring from eggs laid the previous summer on tree stems and branches. By mid-June or so, they are ready to spin cocoons for their transformation into adult moths. Adults emerge around the end of June, mate, lay eggs and die.
Eggs are laid in a dark, shiny mass on small twigs of the tree the caterpillars fed on or similar trees nearby. Those eggs overwinter and hatch the next spring to start the cycle again. The mature eastern tent caterpillar is a large, hairy, dark-colored caterpillar with a yellow stripe down the center of its back. It's often misidentified as a gypsy moth caterpillar, especially when it's left the nest and is looking for a place to make its cocoon. They're easy to tell apart, however. The eastern tent caterpillar has a stripe on its back; the gypsy moth caterpillar, though it's also large, hairy and dark-colored, has spots on its back -- five pairs of blue spots and six pairs of red ones. Another similar species is the forest tent caterpillar, which has a series of yellowish keyhole-shaped spots on its back.
Defoliation by eastern tent caterpillar is rarely a concern unless it occurs in valuable fruit or landscape trees, especially if it occurs year after year. Trees that lose more than 60 percent of their leaves will produce a new set. Repeated use of stored energy in this way may weaken a tree and leave it more vulnerable to other pests, diseases and environmental stresses that ordinarily wouldn't be a problem for a healthy tree. Trees that lose less than 40 percent of their foliage to leaf-eating pests usually suffer no ill effects. Homeowners who don't want to take a chance with valuable fruit trees or ornamentals can remove the tents by hand as soon as they see them and/or spray the foliage with Bacillus thuringiensis, a bacterial disease of caterpillars formulated as a pesticide under a number of trade names. Removing and destroying the shiny, dark-colored, foam-like egg masses from trees anytime after midsummer and before early spring is another effective approach.
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