Webworm nests not a threat to trees

HIAWASSEE, Ga. – It’s the time of year when fall webworms form cocoons in area trees, and although their nests may look like something out of a science-fiction movie, they are harmless.

Fall webworms are attracted to deciduous trees, commonly spinning their nests on hickory, walnut, birch, cherry, and crab-apple. The species is similar to the eastern tent caterpillar, but the fall webworm constructs its nest over the end of the branch rather than at the tree notches. The large conspicuous webs contain caterpillars, partially eaten leaves, and fecal droppings.

While the caterpillars may defoliate a branch or two, they rarely threaten the life of a tree. The leaves they consume would fall soon regardless, and the caterpillar stage of life ends after a few weeks.

Jacob Williams, University of Georgia (UGA) Agricultural-Natural Resource Agent for Towns and Union County, tells FYN that the extension office has received several calls about webworm nests this season.

“I try to discourage people from spraying the nests,” Williams said, “They are not likely to cause any lasting damage to the tree, and the webworms themselves aren’t harmful.”

Fall webworms begin as a pupa in a cocoon under debris on the ground, in bark crevices, and in the soil during the winter months. Adults emerge in summer, and females deposit eggs on tree leaves in masses of 300 to 400. Eggs generally hatch 10 days.

 

The young larvae live as a colony within the balloon-like webs, which contain leaves on which they feed. The webs expand as the larvae grow, and can often measure up to two feet long.

When nearly fully grown, caterpillars often feed outside the web at night. As food becomes scarce on a branch, caterpillars may migrate to another branch or tree. Larvae matures and pupates in the fall.

They are not considered a threat to hardwood forests, nor a threat to the health of infested trees as it occurs after the trees have already stored up much of their food reserves, late in the season.