Fall Webworm
Hyphantria cunea Drury


Hanson, T., and E. B. Walker. [n.d.] Field guide to common insect pests of urban trees in the Northeast. Waterbury, VT: Department of Forests, Parks and Recreation.


Lepidoptera: Arctiidae

Hosts: A wide variety of broad-leaved trees and shrubs, including ash, birch, cherry, willow and elm

Evidence: Look for webs spun by larvae around leaves at the ends of tree branches. Webs are most noticeable in August and September, but empty webs may hang on into winter. On heavily infested trees, several branches may be enveloped by webs. Small trees may be completely enshrouded in webbing. Inside the webs, greenish yellow to brown larvae feed on leaves. Each has a broad, darker band down the back and a yellowish stripe down each side. Bodies are covered with long hairs arising in tufts from orange or black tubercles.

Life Cycle: There is one generation per year in much of the Northeast, with two generations in more southerly areas. Adults are active from May to July. The female lays a mass of several hundred eggs on the underside of a leaf and covers it with hair from her abdomen. The larvae emerge within 10 to 15 days and immediately begin to spin silken webs around the leaves on which they feed. They feed gregariously throughout the summer, gradually enlarging the web to enclose more and more foliage. In early fall, the larvae leave the web to search for places to spin their cocoons. Most pupate in bark crevices, in the leaf litter, or just beneath the soil surface.

a. FALL WEBWORM larvae feed on leaves that they have covered with webbing. Webs are extended to cover more leaves as needed, and feeding is done entirely under the protection of the webbing.

b. The hairy FALL WEBWORM larvae are gregarious until the final molt, when they leave the nest and crawl down the tree to pupate.

Management: Although webs can be an unattractive nuisance, the loss of leaves generally has little effect on the health of the tree because it occurs at the end of the growing season. Rarely, persistent infestations on individual trees may cause branch and top-kill. Fortunately, there are many predators, parasites, and disease organisms that serve as natural controls on webworm populations. If additional controls are necessary, web-bearing branches of small trees may be cut and burned when larvae are still young. Web-bearing foliage may also be sprayed with an insecticide to kill larvae before they cause too much damage.

References:

Drooz, A.T. 1985. Insects of Eastern Forests. USDA Forest Service Miscellaneous Publication 1426. p 225-226;

Johnson, W.T. and Lyon, H.H. 1991. Insects That Feed on Trees and Shrubs. 2nd edition. Cornell University Press. p 166-177;

Martineau, R. 1984. Insects Harmful to Forest Trees . Agriculture Canada Government Publishing Centre, Supply and Services, Ottawa. p 194-196;

Rose, A.H. and Lindquist, O.H. 1997. Insects of Eastern Hardwood Trees. Canadian Forest Service Publication. Forestry Technical Report 29 p 226.

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