Web Spinning Caterpillars
Eastern tent caterpillars and fall webworms both form silken nests in trees. Because of this similarity they are often confused for one another. There are several characteristics that make their differences and proper identification clear. They are found at different times of the year, have different hosts and are found on different places on their hosts.
The eastern tent caterpillar is observed in spring when it’s silken nest is most visible. Their nests are found in the crotches of branches of fruit trees, especially wild cherry, crab apple and apple. They are also but less frequently found on ash, birch, blackgum, redgum, willow, witch-hazel, maple, oak, poplar, cherry, peach, and plum. As many as 150 to 350 eggs are laid in a mass around a twig by female moths in June or July. The caterpillars hatch from the brown varnish-like mass of eggs the following spring and collectively build a nest. The larvae only leave the nest to feed. The final larval instar is also highly visible when it migrates to a new location to pupate, however, they do not feed at this point. There is one generation every year. Trees may be weakened if more than half of the tree is defoliated for three or more years.
Fall webworms are found in late summer and fall creating silken nests around leaves at the ends of branches. All feeding occurs within the silken nests. They will feed on almost all shade, fruit and ornamental trees but true damage to the tree is minimal. Eggs are laid on the undersides of leaves in early to midsummer and hatch in about a week. The caterpillars feed for six weeks before dropping to the ground to pupate. There may be as many as four generations in the south.
In both cases, management techniques are similar. Tents may be removed by hand, or an insecticide with residual activity may be applied to foliage and twigs. Chemical treatments work best on the youngest larvae and will not penetrate the nest. Both species have natural enemies such as birds, stink bugs, wasps, and flies. Use of Bt is also effective against young larvae.
Systemic insecticides may be used on large trees.
Comparison of eastern tent caterpillar and fall webworm.
Eastern Tent Caterpillar
- Tents in spring
- Tents in crotches of branches
- Prefers to feed on fruit trees
- Found east of the Rocky Mountains
- One generation/year
- Tents in summer and fall
- Tents at ends of branches
- Feeds on almost all trees and shrubs
- Found throughout the U.S., Canada and Mexico
- One to four generations/year
Prepared by Janet Kintz, Graduate Research Assistant, and Clyde S. Gorsuch, Extension Entomologist/Professor, Department of Entomology, Soils, and Plant Sciences, Clemson University.
EIIS/TO-11 (New 07/1998).
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