Hyphantria cunea Drury
The fall webworm is a widely distributed native pest of shade trees and shrubs and appears from late summer through early fall. It feeds on almost 90 species of deciduous trees commonly attacking hickory, walnut, birch, cherry, and crabapple. This species acts similarly to the eastern tent caterpillar, but the fall webworm constructs its nest over the end of the branch rather than at tree crotches. The large conspicuous webs contain caterpillars, dead partially eaten leaves, and fecal droppings.
White hair-covered egg masses contain several hundred light yellow eggs. Young larvae are pale yellow with 2 rows of black marks along their bodies. When fully grown, they are covered with whitish hairs that originate from black and orange warts. Larvae (Image 1) vary as to their coloring and markings, but are usually greenish with a broad, dusky stripe along the back with a yellow stripe along the side. The pupal stage is brown. Adult coloration varies considerably from pure white to white with black spots with a wingspread of about 32 mm.
Image 1 - Fall webworm larva -
J.B. Hanson - USDA Forest Service; UGA0949061b
This pest overwinters as a pupa in a cocoon that is concealed in ground litter, cracks and crevices, or in the soil. Adults first appear in mid-June but may continue to emerge in small numbers during most of the summer. Females usually deposit their egg masses on the undersurface of the leaves. Larvae hatch in approximately 7 days. They immediately begin to spin a small silken web over the foliage on which they feed. As they grow, they enlarge the web to enclose more and more foliage (Image 2). The remains of these nests may persist through winter. These webs may sometimes surround 2-3 feet of infested branch. Larvae are gregarious and feed together until the last molt, after which they may feed independently. Larvae mature in about 6 weeks. Mature larvae leave the web and pupate on or in the soil. There may be one or two generations each year, depending on the geographic location in Pennsylvania.
Image 2 - Fall webworm larva -
J.B. Hanson - USDA Forest Service; UGA0949061b
The larval stage of this pest skeletonizes and consumes leaves inside the protection of a tent-like web that they enlarge as they require additional food and grow. They may defoliate a tree occasionally, but rarely kill it. On shade trees webs usually occur on occasional branches. They may not injure the tree appreciably, but they reduce its ornamental value.
Various species of natural enemies help to manage this native insect. Birds and many insect predators and parasitoids attack the larval stage. Eggs may also be destroyed by predators and insect parasitoids. It is possible to reduce this pest's population by mechanical control. When the webbed branches are within reach, they can be pruned and destroyed. This may be practical if the webs have not become too large and the aesthetic shape of the woody ornamental plant is not reduced by pruning.
Apply a registered insecticide when webs and larvae are small. This usually occurs sometime during July. The entire infested plant does not need to be treated. Only the webs and their associated foliage should be thoroughly covered.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Authored by: Gregory A. Hoover, Sr. Extension Associate
Penn State College of Agricultural Sciences research, extension, and resident education programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
Visit Penn State Extension on the web: http://extension.psu.edu
Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied.
This publication is available in alternative media on request.
The Pennsylvania State University is committed to the policy that all persons shall have equal access to programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualifications as determined by University policy or by state or federal authorities. It is the policy of the University to maintain an academic and work environment free of discrimination, including harassment. The Pennsylvania State University prohibits discrimination and harassment against any person because of age, ancestry, color, disability or handicap, national origin, race, religious creed, sex, sexual orientation, gender identity, or veteran status. Discrimination or harassment against faculty, staff, or students will not be tolerated at The Pennsylvania State University. Direct all inquiries regarding the nondiscrimination policy to the Affirmative Action Director, The Pennsylvania State University, 328 Boucke Building, University Park, PA 16802-5901; Tel 814-865-4700/V, 814-863-1150/ TTY.
© The Pennsylvania State University 2013