Marion 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 appearing on our trees’ foliage and shrubs. The eastern tent caterpillar, Malacosoma americanum, is a native pest of North America. Their populations fluctuate yearly, with significant outbreaks occurring every several years. They feed on many hardwood species. Its damage does not kill trees; 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, sweet gum, and 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 yearly in the spring when wild cherry trees bud out. As they hatch, these social insects gather together to spin a nest in the forks of a tree. The caterpillars feed on tree foliage during the early morning and evenings, returning to the nest during the day’s heat and rainy weather for protection.
The larva (caterpillars) are brightly colored with long hairs on their bodies, mainly along the sides. Colors 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. Their wandering can be of concern to homeowners when they encounter these caterpillars in large numbers. Cocoons can be found under bark, in a rolled leaf, or in dead plant material on the ground. After a few weeks, the adult emerges as a reddish-brown moth from the cocoon. 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 several parasitic wasps. The homeowner may opt for physical removal or pruning if the tents safely reach the solid, level ground. Tents can also be broken open to expose larvae to predators. Larva larger than 1/4 inch in length and those beneath the webbing are difficult to control with a pesticide. These pests are mostly a nuisance, and control is seldom warranted. If power is necessary, choose a pesticide with a low environmental impact. 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.
Remember, pesticides are poisonous. Always read and follow pesticide recommendations. The pesticide label is the law! Outbreaks of Eastern tent caterpillars are periodic and short-lived, and damage is generally considered aesthetic rather than a health threat to trees and shrubs.
See Eastern Tent Caterpillars Fact sheet at the Clemson Home and Garden Information Center at: https://hgic.clemson.edu/
For more home and garden information, contact your local Clemson Extension Office.
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