The trees in our New Hampshire town are covered with ugly cocoonlike things that look as if they’re destroying the foliage. What are these?
Most likely you’re seeing the webs of fall webworms, also called bagworms or eastern tent caterpillars. These can appear from late July through October. The caterpillars are greenish yellow with lots of hair and black dots, and they feed on leaves. As feeding continues, their silken webs enlarge to cover the areas they plan to eat. This can indeed make it look as if the tree is being destroyed. Insecticides can control the worms, but each web must be penetrated for success. Infected branches also can be removed and the caterpillar webs destroyed. Bad as the webs may look, however, the damage they cause is usually minimal, and most leaves will return the following spring.