How can I control tent caterpillars?
Eastern tent caterpillars (Malacosoma americanum) are native to the eastern half of North America, including New York State. They feed on tree leaves in the spring, preferring a variety of fruit trees. Their highly noticeable white silk nests usually appear in the forks of tree branches in spring. Feeding on new leaves, one or two colonies of these caterpillars can completely defoliate a small tree.
Tent caterpillars are sometimes confused with fall webworms. The webworm's nests arrive in the fall, not spring, and are spun at the ends of branches rather than in tree crotches.
Tent caterpillars hatch at bud break. They consume new tree leaves by day and then return to their nest at night. After 6-8 weeks, they pupate, develop into moths, lay eggs, and die, leaving behind dark gray, foam-like, circular egg cases on tree branches, awaiting the following spring.
A native and natural part of our ecosystem, these caterpillars will always be around, sometimes in small, unnoticeable numbers. However, dense concentrations of tent caterpillars can cause a decline in trees' health or threaten an economic resource. There are several options for dealing with these pests:
- Do nothing. Healthy deciduous trees usually survive defoliation and grow a second set of leaves in July. Trees can stand 2-3 years of defoliation, although their vigor and resistance will be weakened.
- Hand removal: If you can reach them, the nests can easily be removed with gloved hands or using a tool or stick, wrapping nest around the stick.This is best done in early morning or late afternoon, when the caterpillars are likely to be in the nest. Removed egg masses, tents and pupae should be dropped into a container of soapy water.
- Tree wraps: Trunks of trees can be wrapped with a sticky material to trap the caterpillars as they move up and down the tree. The caterpillars can then be removed and destroyed. Alternatively, a folded band of burlap (folded edge up) will catch the caterpillars as they climb up the tree, enabling easy removal.
- Sprays: These fall into two categories: microbial/biological pesticides and chemical sprays. Microbial and biological pesticides contain living organisms which the young caterpillars eat; they work best on young caterpillars. The most common of these is Bacillus thuringiensis (Bt). Naturally occurring in soil and on plants, Bt is harmless to people, animals and plants, but does affect young moth and butterfly larvae. When Bt is eaten, the caterpillar becomes paralyzed, stops feeding, and dies of starvation or disease. Chemical sprays, on the other hand, are contact poisons. They can kill beneficial insects, nesting birds and other animals.
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- Courtesy of NYBG Plant Information Service