Eastern Tent Caterpillars | |
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| April 28, 1999 | |
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Eastern tent caterpillars are present throughout the state. Some of the tents in southern Illinois are already several inches across and contain older caterpillars. Even in the southern part of the state, late-hatching eggs are responsible for small webs with young caterpillars as well. At The Morton Arboretum they are about 1/4 inch long, indicating that they haven’t been out long. They will grow to 2 inches and become hairy with a white stripe down their backs and blue spots between longitudinal yellow lines. The larvae gather at a fork of a tree and build a web or “tent,” but they leave the web to feed. Because they create a strand of silk wherever they go, the web enlarges as the caterpillars eat. Severe defoliation only occurs when populations are high.
Control the caterpillar by tearing or pruning the webs out of the tree. This should be done when the caterpillars are in the nest and not out feeding; we suggest cloudy or rainy days or at night. Another option is to remove the overwintering egg masses before spring if you can find them. The egg masses are dark gray to black and are wrapped around twigs that are about the circumference of a pencil. Bacillus thuringiensis kurstaki (Bt) can also be sprayed on young larvae, but it will not kill mature larvae. For other chemical recommendations, refer to the Illinois Commercial Landscape Turfgrass Pest & Management Handbook, 1998–1999. (The Morton Arboretum and Phil Nixon)
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| Author: | Phil Nixon staff at The Morton Arboretum |
