Silken caterpillar nests that look like cobwebs are hanging in the cottonwood trees, and literally thousands of caterpillars are all over the pavilion area, in the Upper Deschutes Day-use Area. Fall webworm caterpillars work together to make the gauzy looking nests. These caterpillars are the larvae of a native species of tiger moth known to entomologists as (Hyphantria cunea). They are considered to be a pest by many people, but are primarily a cosmetic nuisance, according to Oregon State University. Fall Webworm is a native insect; their population ebbs and flows over time. Some years have heavier infestations and this appears to be one of those years. The caterpillars feed on more than 85 species of deciduous trees and shrubs in the United States and are commonly seen in black walnut trees, willows, fruit trees and cottonwoods in Oregon. It is one of the few insect pests introduced from North America into other continents.
Like many insects, the Fall Webworm has several different appearances during it’s lifecycle. Webworm caterpillars, related to wooly bear caterpillars, are black with yellow to golden-orange bumps under a cloak of long tufted white hairs. They grow to about 1.5 inches long.
Then overwinter as pupae in a brown cocoon in protected places, such as in bark crevices or on the ground in litter or duff. This species acts similarly to the eastern tent caterpillar, but the Fall Webworm constructs its nest over the end of the branch rather than at tree crotches.
The adult, a large silky white tiger moth with black spots on its underside, flies in mid-summer. After mating, the female moth will lay hundreds of yellow or white eggs on the undersides of leaves. Like most moths, the Fall Webworm moths are nocturnal and are attracted to light. Adult moths have a wingspan of between 1.4–1.7 inches. Adults emerge in spring after host plants have developed leaves and mate. female moths deposit eggs in masses Adults emerge in spring after host plants have developed leaves and mate. Female moths deposit eggs in masses under leaves that appear covered with hair.
So, if you visit the park, look into the cottonwood trees and you will see these nests as well as little fuzzy caterpillars.