Eastern Tent Caterpillars

By on September 30, 2016

Eastern Tent Caterpillars

Landscape & Garden Editor Kevin Johnson Says Fall and 
Winter are the Best Times to Gain Control of This Pest

The past few months we’ve been seeing quite an outbreak of Web Worms throughout the area, and we’ll cover those later, but for now we’re going to get a jump on spring and talk about the Eastern Tent Caterpillar. I’ve heard them called bag worms– not true– they are Eastern Tent Caterpillars. The goal of this article is to become more familiar with the life cycle of these leaf-eating machines and how to take control now in preparation for spring.


The Eastern Tent Caterpillar, Malacosoma americanum, is a pest native to North America and is the larvae of a moth, which is rarely seen. In the larvae stage they are defoliators of deciduous trees. The caterpillars will grow in length from 2-2 1/2 inches at maturity. They are black and hairy with a white stripe down their back with a brown or yellow strip down their sides, along with some oval blue spots. They are typically found on both wild and ornamental cherry trees as well as on apple and crabapples, however they also nest in other fruit and hardwood trees at times.

Life Cycle

Eastern Tent Caterpillar overwinters as an egg. The egg mass consists of 150-400 eggs and is covered with a black shiny material. Egg masses can be found on tree branches about the width of a pencil in diameter or less. They then typically hatch in March as larvae, which again is the caterpillar stage. That’s when they begin to build their silky tent in the crotch of trees (web worms build their tents at the ends of branches). The caterpillars emerge from the protection of their tents to feed in the morning and at night, this is when leaf damage is done. Four to six weeks later, caterpillars leave the nest individually and find a place to spin a cocoon. It’s important to note that they are not feeding or causing damage at this point. They’re searching for a safe place to begin the next phase of their life cycle. Roughly three weeks from spinning their cocoons, the moth emerges. These moths are strictly nocturnal. They mate, the female lays eggs on the small branches and the process repeats itself. There is only one generation per year.

Control and Management

Prevention and early control is important. The best method of control is removing the egg masses from your fruit and ornamental trees. This is done once trees are devoid of leaves in the fall or winter and will reduce the caterpillar population before they hatch. You can just scrape the egg masses off with your fingernail. In the early spring, pruning out the tent is another option if you can reach it. Natural predators such as birds, parasitic wasps and disease also help control their population. Water based insecticides generally wont penetrate their nests, and really aren’t a good idea unless you get them early.

The Good News

Like many things in nature, Eastern Tent Caterpillar populations fluctuate from year to year. This year we had a significant outbreak. Let’s see what next year brings. Oh, and your trees that have been defoliated– it’s unlikely they will die– they will usually recover and put out a new crop of leaves. Let’s just learn to live with the problem because there’s nothing we can really do anyway.

Kevin Johnson is the owner of Green Leaf Lawn and Ornamental, LLC, based in Blue Ridge. For more information about the devastating hemlock woolly adelgid and treatment options, Kevin can be reached toll free at 866. 883. 2420 or by email at growitgreen@etcmail.com. Or check out his web site at www.wetreatlawns.com or visit www.hemlocks.org for more info.