Fall webworm moths, Hyphantria cunea, are medium sized (1.2-1.5 inch wingspan) snow-white insects with or without black spots. Tiny, round, greenish to yellow eggs are laid in masses of several hundred on the undersides of leaves. As the eggs are laid, hairs from the body of the moth stick to them and obscure and perhaps protect them. Tiny, hairy caterpillars hatch and grow into pale to dark caterpillars about 1¹/₂ inches long that are covered with long hairs. One race of fall webworms has black head and the other has rusty-orange heads. The pupa is dark brown, cylindrical, and about ¹/₂ inch long. The pupa is surrounded by an almost transparent cocoon that has hairs mixed in. These caterpillars begin their webs from the ends of the branches, not from the crotches of the tree as do eastern tent caterpillars.

Fall webworm moths are snow-white although some have spots.

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Fall webworm moths are snow-white although some have spots.

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Fall webworm moths lay hundreds of eggs.

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Fall webworm moths lay hundreds of eggs.

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These are young fall webworms.

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These are young fall webworms.

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Fall webworms have long setae that irritate sensitive people.

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Fall webworms have long setae that irritate sensitive people.

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Fall webworm webs can be quite large and hold many caterpillars.

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Fall webworm webs can be quite large and hold many caterpillars.

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Cocoons of fall webworms incorporate the caterpillar's long setae.

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Cocoons of fall webworms incorporate the caterpillar's long setae.

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Fall webworms occur throughout North America, Japan and Korea. They were accidentally introduced into Europe in 1946 where it is considered to be a worse pest than the gypsy moth. Fall webworms feed on over 600 species of trees and shrubs. In North Carolina they are most often found on sourwood, persimmon and pecan. Fall webworms primarily cause cosmetic damage to shade trees because of the unsightly webs they form around the foliage on which they feed. Young caterpillars eat leaf surfaces so that only the tiny veins remain. This residue turns brown and collects in the web. Older caterpillars devour the entire leaf. Because they are most abundant in mid-late summer after the tree has had some time to store food and the weather is hot and rainfall less, the a tree's life is rarely in danger.

Fall webworms overwinter as pupae in cocoons hidden in mulch, leaf litter and in the soil. Moths emerge from these cocoons from mid-March to mid-April during evening hours. They mate and each female may lay up to 900 eggs laid in a mass on the underside of a leaf. Eggs hatch in about 7 days. The tiny new caterpillars form their web and feed gregariously protected within. As they grow, they molt six times and the web mass becomes filled with shed skins, droppings and dead leaves. The web is enlarged to encompass fresh leaves and may be expanded 2 to 3 feet long. Small trees infested with several web masses may become completely enveloped. After feeding for 4 to 5 weeks, the caterpillars crawl down, spin cocoons and pupate in mulch or soil. In July and August, another generation may develop. There is some evidence that this "second generation" is really another race. Fall webworms overwinter as pupae in their cocoons below the tree, but the webs may remain in the tree through most of the winter before weathering away.

A small persimmon tree completely webbed over by fall webworms.

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A small persimmon tree completely webbed over by fall webworms.

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Fall webworms occur throughout North America, Japan and Korea. They were accidentally introduced into Europe in 1946 where fall webworms are considered to be worst than gypsy moths. Fall webworms feed on over 600 species of trees and shrubs. In North Carolina they are most often found on sourwood, persimmon and pecan. Fall webworms primarily cause cosmetic damage to shade trees because of the unsightly webs they form around the foliage on which they feed.

Fall webworms can be easily destroyed or disrupted by pulling down the webs and destroying he caterpillars if the webs are within reach of a stick or pole. This also exposes caterpillars to bird and wasp predation. If the webs are beyond easy reach and control is deemed desirable, a trombone sprayer or power sprayer may be able to reach higher in a tree. Beyond that, professional arborists or landscapers may be required. The important point to remember in spraying is to cover the foliage closest to the web mass. Spraying the web itself does not give good contact with the caterpillars. Consult the North Carolina Agricultural Chemicals Manual listed below for other chemicals.

Figure 4. Fall webworm webs.

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Figure 4. Fall webworm webs.

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• Common name: fall webworm, scientific name: Hyphantria cunea (Drury) (Insecta: Lepidoptera: Erebidae: Arctiinae). Andrei Sourakov, A. and T. Paris, 2011 (revised). Featured Creatures, Entomology & Nematology | FDACS/DPI | EDIS, University of Florida Publication Number: EENY-486.
• Fall Webworms Hatching. Frank, S. 2011. NCSU College of Agr. & Life Sci. North Carlina Pest News 26 (12): 7.
• Fall Webworm, Wraps branches in silk in late summer. Anonymous. 2011. USDA Forest Service, Forest Health Protection, Rocky Mountain Region.
• NC State Extension Plant Pathology Publications and Factsheets
• NC State Horticultural Science Publications
• North Carolina Agricultural Chemicals Manual

For assistance with a specific problem, contact your local Cooperative Extension center.