The ugly nest caterpillar, which is yellow-green with a dark head, is most commonly found on chokecherry and black cherry, but they will feed on other hardwood trees and some shrubs. These caterpillars spin dense, unsightly silk tents (Figure 1) that are messier versions of those made by fall webworms; tents are located in the tops of plants. The webbing, pieces of leaves, and large amounts of accumulated frass earn the insect its common name.
While their impact is mostly aesthetic, terminals bound by the webs can remain distorted in subsequent years. There is one generation each year, but eggs may be laid from mid-summer until fall.
Mimosa webworm caterpillars affect honeylocust, as well as mimosa. These caterpillars tie together leaves of their host. A generation should be well along now with a second one in late July. These caterpillars are gray to dark brown with white stripes running the length of their bodies. Fully grown worms are just over ½ inch long.
When practical, pull off or physically crush the nest with the worms inside to end the damage. Pruning off developing nests also is effective.
By Lee Townsend, Extension Entomologist