Fall Webworms

Fall webworm is a conspicuous insect that is affecting several plant species in Great Basin National Park. Webworms are caterpillars that feed on many types of deciduous trees. Within the park, they make their homes on cottonwoods and chokecherry.

The caterpillars emerge in August and September and immediately begin feeding on leaves. They also begin constructing a siken web or tent in the branches of their host tree that surrounds the foliage they will consume. The tent is used as a feeding area and a resting place for the caterpillars, and it is made larger to include more foliage, and to accomodate the growing insects. Fall webworms can totally defoliate a tree, which may impair the tree's ability to grow, but rarely kills it.

The caterpillars spend winter in the pupal stage hidden under tree bark, soil, or leaf litter and will emerge the following spring as moths ready to produce another generation of webworms.

Affected Areas in the Park

In the summer of 2006, fall webworm defoliated many of the cottonwoods along Snake Creek, leaving bare branches covered with their silken webs. Some of the chokecherry bushes that line Baker Creek Road above the campground have also been affected.