Contact: Eric Day, Manager, Insect Identification Laboratory
Publication 444-246, August 1996
Distribution and Hosts
Native to North America, the fall webworm occurs throughout the
United States and southern Canada. Its hosts include more than
100 species of deciduous forest, shade, and fruit trees, with
preferences varying from region to region.
Description of Damage
Newly emerged larvae immediately begin to spin a silken web over
foliage on the terminal portions of the branches. The larvae
feed on the leaves within the webs. As the larvae grow, webs
enlarge and enclose more foliage. Large portions of tree
branches are commonly enclosed by such webs, and are most
apparent from mid- to late-summer. Early stage larvae feed on
the upper surfaces of the leaves, and late instar larvae eat
entire leaves except for larger veins and midribs. The insect is
considered an ornamental pest due to the unsightliness of the
webs; however, it is ordinarily of no great importance as a
Eggs are small, yellow or light green, and usually located in
hair-covered masses on the underside of leaves. Mature larvae
are 25-31 mm long and covered with silky hairs. Their color
varies from pale yellow to green, with a black stripe on the back
and a yellow stripe on each side. Head color varies from red to
black. Pupation occurs in thin cocoons usually spun in the duff
or just beneath the surface of the soil. The adult moth has a
wingspan of 25-31 mm and is snowy white, usually with dark spots
on the wings.
From May to July, adult moths lay their eggs. Eggs hatch within
two weeks and the larvae immediately begin feeding and
constructing webs. Larvae feed and webs continue to enlarge for
four to eight weeks. There are at least two generations per year
in the South.
More than 50 species of insect parasitoids and 36 species of
predators of the fall webworm are known in the U.S., yet they are
not commercially available. On small trees, nests can be cut out
and destroyed. Soap or other insecticides may be applied from
mid- to late- summer. Consult the Pest Management Guide for
Horticultural and Forest Crops, Virginia Cooperative Extension
Anonymous. 1989. Insects and Diseases of Trees in the South.
U.S.D.A. Forest Service Protection Report R8-PR16.
Drooz, A.T. 1985. Insects of Eastern Forests. U.S.D.A. Forest
Service Miscellaneous Publication No. 1426. 605 pp.
Johnson, W.T. and H.H. Lyon. 1991. Insects that Feed on Trees
and Shrubs. Cornell Univ. Press. N.Y. 560 pp.