Ornamental & Turf Insect Note Logo

Fall Webworm

Stephen Bambara & James R. Baker

CAUTION: This information was developed for North Carolina and may not apply to other areas.
Hyphantria cunea (Drury), Arctiidae, LEPIDOPTERA

General Information

Fall webworm moths are medium sized (1.2-1.5 inches) snow white insects with black spots. Tiny, round, 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 protect them.

Tiny, hairy caterpillars hatch and grow into pale to dark caterpillars about 1.5 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 and cylindrical and about 0.5 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. They are sometimes confused with tent caterpillars and bagworms.

Biology

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.

Control

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. (View a QuickTime movie.) 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 along with a check book.   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 NC Agr. Chemicals Manual listed below for other chemicals.

Pesticide (Trade Name) 
Remarks
acephate (Orthene)
(Orthene TTO,*various Ortho products)
Follow label directions
Bacillus thuringiensis; B.t., Dipel, Thuricide, others) Apply to foliage adjacent to web.
chlorantraniliprole (Acelepryn) Foliar and systemic.
*carbaryl (Sevin)  Follow label directions.  Apply to adjacent foliage.
bifenthrin (Talstar Lawn&Tree)  Follow label directions.  Apply to adjacent foliage.

* formulations suitable for home use.


Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance contact an agent of the North Carolina Cooperative Extension Service in your county.
© 2001 NC Cooperative Extension Service

Prepared by: Stephen Bambara and James R. Baker*, Extension Entomologists
*emeritus
ENT/ort-46 January 1995 (Revised) 2006

Web page last reviewed January, 2011 by webperson.