Fall Webworm Larvae

Description:

The larvae (caterpillars) of the Fall Webworm Moth measure up to 35 mm long. Their colors are highly variable running the gamut from pale green, dingy yellow, or brownish with dark spots and/or stripes. They are covered with white tufts of hair. Those pictured measured 15-25 mm in length with several sizes represented in the same web. You can see the variation in color, even within the same web with all being a shade of light green on the sides but varying between points of black on some to a solid black stripe on the dorsum of others. Looking at the tree, Fall Webworm is easily distinguished from Tent Caterpillars and Bagworms as their webs are unique to Webwoms. For the differences see the bottom reference to the right. For images of the (mostly) white adult moth see the Wiki reference on the right. The life cycle consists of the adult moth laying eggs on the underside of leaves in the late summer or early fall, the larvae appearing about a week later. The young caterpillars make small webs around a few leaves, later making larger webs around more and more leaves, sometimes covering entire branch-ends. 4-6 weeks later they fall to the ground where they pupate under leaf litter, bark or in the ground.

Habitat:

The Fall Webworm is found throughout North America from Mexico to Canada. Although it favors cottonwood, walnut and ornamental fruit trees, it can be found on more than 100 deciduous trees and shrubs.

Notes:

Upon returning from a week in the mountains of Colorado, I noticed 2 of our trees covered with webs. So I investigated. The main problem with webworms is aesthetic: trees look horrible with their webs encasing “dead” branches and containing dried up leaves and caterpillar excrement. While they may seriously damage younger, smaller trees, no real harm is usually done to larger trees. It is definitely a pest. I’ve seen several trees in our neighborhood sporting these webs.