Web Worms & Black Walnut Trees

Webworms build their nests in up to 85 tree species, but prefer black walnut, according to Jeff Miller of Oregon State University. These caterpillars craft visible webs during the fall months.

Identification

White hairs protrude from the black, orange-spotted body of the webworm caterpillar. Webworms build nests at the end of branches, ensuring that a food source stays protected within the web. Webworm caterpillars spin brown cocoons, eventually transforming into a white moth with black spots during the following summer.

Effects

Webworms create an unattractive appearance in black walnut trees, but do not create long-term harm. While webworms eat the leaves of the tree, they do so after the growing season when the tree begins to store energy for the winter.

Solution

Blasting trees with a jet of water removes the nest but simply spreads the webworms to other branches of the black walnut tree, where they promptly make new webs. Experts at the University of Oregon North Willamette Research and Extension Center recommend pruning affected branches and dipping them in soapy water before disposal.

References

• Oregon State University Extension: Fall Webworms Enclose Themselves and Tree Branches
• Ohio Department of Natural Resources: Bagworms, Webworms, or What?