The Q&A Archives: Caterpillars In Trees

Question: I looked up in one of my trees and saw a translucent silken pillow crawling with caterpillars. If I decide NOT to shoot a horror film, how do I get rid of these creepy crawlers?

Answer: There are two types of pests that fit your description: tent caterpillars and webworms. Tent caterpillars spin their silken nests in the crotches of limbs. Fall webworm nests are located at the ends of the branches, and their loosely woven webs enclose foliage while the tents of the tent caterpillar generally do not. Tent caterpillars are more common in the spring, while fall webworms, as their name implies, arrive later in the season.

Adult tent caterpillarss are moths that lay eggs on tree twigs in the summer. The eggs overwinter, then the caterpillars hatch in early spring. They spin a silk tent for protection, leaving the tent at night to feed. After feeding for 5 to 8 weeks, they travel down the trunk to pupate in leaf litter.

Webworms overwinter in the pupal stage. Adults emerge late June to mid July; females lay large egg masses on the undersides of leaves. Eggs hatch into larvae after about 10 days. Larvae feed until late summer or early fall.

There are a number of ways to control them. If you're brave, you can pull the webs out of the branches (wearing gloves!). Or you can prune affected branches and burn them. The best way to keep the pests in check is to inspect ornamentals and trees in the winter and remove any egg masses. Continue inspecting plants and, in early spring, remove any small tents you find.

Young caterpillars can be controlled with the organic pesticide B.t. var. kurstaki (sold under various trade names). This bacteria kills the caterpillars but will not harm you, the birds, bees, animals and other insects in the garden. You must catch the pest early, however. Once the larvae are protected by their webs they are difficult to reach with an insecticide.

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