Tent Caterpillars

By, Kevin Cutlip

Tent caterpillars overwinter as eggs in an egg mass. The eggs hatch in the spring, about the time wild cherry leaves begin to unfold. The young caterpillars quickly gather at a branch fork or crotch and begin to build a silk web. The larvae leave their tent to feed on foliage. Young caterpillars feed during the day and remain in the tent at night. Older (and larger) caterpillars feed at night and remain in the tent during the day.

While tent caterpillars can nearly defoliate a tree when numerous, the tree will usually recover and put out a new crop of leaves. In the landscape, however, nests can become an eyesore, particularly when exposed by excessive defoliation. The silken nests are built in the crotches of limbs and can become quite large.

Eastern tent caterpillar nests are frequently confused with fall web worm nests. Unlike the tent caterpillar, fall web worm nests are located at the ends of the branches and their loosely woven webs enclose foliage, while the tents of the eastern tent caterpillar do not. While there may be some overlap, fall web worm generally occur later in the season.

Larvae cause considerable concern when they begin to wander to protected places to pupate. They are frequently seen crawling on other types of plants, walkways, and storage buildings. They are a nuisance and can create a mess when they are squashed on driveways, sidewalks, and patios. Keep in mind, though, that no additional feeding or damage is done by the wandering caterpillars.

Adult eastern tent caterpillars (1-1/2 inches long) are reddish brown moths with two white bands running diagonally across each fore wing. Host plants include cherry, apple and crab apple, but may be found on a variety of shade trees as well.

Tent Caterpillar Control

• Scrape off and discard overwintering egg masses and tear the protective tents out by hand before the larvae start to feed.
• Control caterpillar movement and restrict access to feeding areas with Sticky Tree Bands or Tanglefoot Pest Barrier.
• Apply Bacillus thuringiensis, var. kurstaki (Bt-k) or Monterey Garden Insect Spray (Spinosad) to the leaves to kill feeding caterpillars.
• If necessary, spot treat with plant-derived insecticides as a last resort. Spray must penetrate silken tents for effective control.

Integrated Pest Management Strategies

• Live with the problem. It is not necessary to spray insecticides to control the eastern tent caterpillar. Healthy defoliated trees will grow new leaves. Infested trees can be unsightly and are less vigorous than attacked trees, but they are seldom killed. Typical natural controls include birds, predacious and parasitic insects (especially wasps), and disease organisms. Caterpillars with white eggs or cocoons attached to their back should not be destroyed because they are being hosts for native parasites.
• Hand pick egg masses. Future damage on small trees can be reduced by locating and removing egg masses during winter because they are most obvious at that time. They can be scraped off with a thumbnail or pruned out.
•  Apply insecticides. If insecticide sprays are necessary, they should be applied when the tents are first noticed. Caterpillars leave the tents to feed, so thorough coverage of the foliage with the insecticidal spray will provide control. Tents are water repellent, so spraying them with water based insecticides is not very effective. Insecticides that can be used include Bacillus thuringiensis (Bt, Dipel or Thuricide), carbaryl (Sevin), pyrethrins, acephate (Orthene) or spinosad.
• Let the predator alone. Ever notice that Wasps show up around the same time? Their favorite food is Tent Caterpillars.