Around the Countryside

Eastern Tent Caterpillars InvMarion Barnes, Senior County Extension Agent

Clemson University

Spring has arrived in the low country, home gardeners are working in their gardens, azaleas and dogwoods have been blooming for several weeks, and tent caterpillars are making their appearance on the foliage of our trees and shrubs. The eastern tent caterpillar, Malacosoma americanum, is a native pest of North America. Their populations fluctuate from year to year, with significant outbreaks occurring every several years. They feed on many hardwood species. Its damage does not kill trees, but some twig and foliage loss may occur. Some homeowners find their unsightly, silken-like tent structures in the forks of trees unattractive. Their large numbers can become a nuisance as they crawl over plants, sidewalks, and structures. Oaks, wild cherry, wild plum, crab apple, and sweet gum, as well as many hardwood trees, are some of their favorite habitats.

The eastern tent caterpillar overwinters as an egg within an egg mass on small tree branches and may contain as many as 400 eggs. The larva usually emerges in the spring each year, about the time wild cherry trees start to but out. As they hatch, these social insects gather together to spin a nest in the forks of a tree. The caterpillars tend to feed on tree foliage during the early morning and evenings, returning to the nest during the day’s heat and during rainy weather for protection.

The larva (caterpillars) are brightly colored with long hairs on their bodies, mainly along the sides. Colors tend to vary with blueish, tan, white, orange, and black markings. At maturity, caterpillars can reach one and a half to two inches in length.

For about 4 to 6 weeks, the caterpillars feed, grow and expand their nests, then scatter, spin cocoons of woven whitish or yellow silk and pupate. Cocoons can be found under bark, rolled leaves, or dead plant material on the ground. After a few weeks, the adult emerges from the cocoon as a reddish-brown moth. They mate, and the female lays eggs on small branches that will hatch next spring, starting the cycle again.

Caterpillar populations are generally controlled by numerous natural enemies, such as predators (birds, other insects), diseases (viral, fungal, bacterial), and many parasitic wasps. The homeowner may opt for physical removal or pruning if the tents can be reached safely from solid, level ground. Tents can also be broken open to expose larva to predators.

If treatment with an insecticide is warranted, keep in mind that larva larger than 1/4 inch in length and those beneath the webbing are challenging to control with a pesticide. When choosing a pesticide, consider one that has a low impact on the environment. Be mindful of pollinators when applying pesticides. Products such as Bt (Bacillus thuringiensis), which are less toxic to beneficial insects, are an option for trees that are flowering and being visited by pollinators. Always read and follow pesticide recommendations. For more home and garden information, contact your local Clemson Extension Office.

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