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
Did You Know?
The Sagebrush, a very common resident of Great Basin National Park, is well adapted to the area. The Big Sagebrush root system can extend as much as 90 feet in circumference. This adaptation allows the plant to collect as much water as possible during infrequent rains.