Wildlife Watching Wednesday: The Native Forest Tent Caterpillar

By: Tom Berg

Caterpillars are cool creatures. They hatch from tiny eggs and usually grow through multiple stages, or instars, before going through the amazing process of metamorphosis and turning into a beautiful butterfly or moth. Caterpillars can be green, blue, red, orange, yellow, white, brown, black – almost any color of the rainbow. Most are made up of a combination of colors, too.

Some caterpillars are cooler than others, though, for sure. Some of the caterpillar species that people tend to dislike are the various “tent” caterpillars. Some of these tent caterpillars, like the Spongy Moth Caterpillar, are non-native species and are quite destructive. The Forest Tent Caterpillar, however, is a native species and plays an important role in the environment.

Forest tent caterpillars are mostly blue, with light cream-colored or yellowish spots on their backs. They also have thin orangish-yellow stripes along their sides and lots of fine hairs on their sides near their feet. These hairs can cause skin irritation to people if they come into contact with them. Fully developed forest tent caterpillars are about two inches long before they pupate and turn into a moth.

Unlike other tent caterpillars that form large web-like tents which cover large sections of trees and bushes, forest tent caterpillars do not make silk tents. Instead, they lace a thin sheet of silk on the trunk of their host tree where they feed and molt. The feeding caterpillars can eat large percentages of the leaves on the trees, but most trees replace the lost leaves within a month or so and sustain little or no permanent damage.

Forest tent caterpillars prefer oak, aspen and maple trees as their host trees. Luckily, these caterpillars are kept in check by natural predators like birds which feed on them extensively. Warblers, bluebirds and American Robins eat many forest tent caterpillars. Wasps like yellow jackets (and others) also hunt the caterpillars, and spiders, ladybugs and lacewings also help keep them in check.

Despite the temporary loss of leaves experienced by their host trees, our native forest tent caterpillars are actually beneficial to the environment. They provide a ready food source for a wide variety of wildlife as mentioned above. More than 50 species of birds eat these caterpillars in the springtime and feed them to their fast-growing chicks. Bats have even been known to eat them at night!

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