The eastern tent caterpillar is the larval stage of a moth that belongs to the family, Lasiocampidae. The adult is brown with two prominent, lighter-colored stripes that run across its forewing. This moth has feathery antennae and a furry appearance.
But it is in the larval stage that this pest does damage to your trees. The caterpillars attack certain host trees after hatching; they can eat a substantial percentage of the leaves on the tree. A small infestation is unlikely to kill a mature, healthy tree; the tree will grow a new set of leaves. But a large infestation can cause damage that is fatal to young and/or stressed-out specimens. Even in the case of a mature, healthy tree, the stress involved in growing a new set of leaves, if followed by dire circumstances such as the onset of a severe drought or an infestation of another pest or disease, can prove fatal.
What Do Eastern Tent Caterpillars Look Like?
The caterpillars are black when young. As they grow to maturity (and an eventual length of 2 inches), they develop more distinctive characteristics:
- Hairs bristling out of the sides of their bodies
- Blue or orange flecks
- A white stripe running down their backs
4 Ways to Control the Eastern Tent Caterpillar
There are a number of different ways to get rid of an active infestation. While pesticides are one option, many gardeners choose safer and less expensive options:
Remove the Tents Manually
Wearing work gloves, remove the silky "tents" and the caterpillars within them by hand, put them in a bag, squish them, and dispose of them.
Remove the Eggs Manually
You can also look for eggs on the branches earlier in the season and either crush them or prune off the branches that they are attached to. Removing the eggs manually has two advantages over removing the tents manually. First, you can nip the problem in the bud, before you have a full-scale infestation on your hands. Second, some gardeners would be squeamish about touching the caterpillars, themselves, even with gloves on; touching the eggs is a bit more palatable.
Inspect the branches of host trees for egg masses by early spring, before the eggs hatch. The egg mass of the eastern tent caterpillar encircles small branches. It is black, shiny, and looks a bit like a jellybean. Even if, upon finding such a mass, you are not sure that it is the egg mass of the eastern tent caterpillar, it does no harm to remove it (to be on the safe side).
Apply a Pesticide
If you are going to apply a pesticide to control eastern tent caterpillars, do so when they are still young. These pests become more resistant to pesticides when they grow bigger and stronger. Insecticidal soaps are best because they are safer than many other pesticides are. Apply them directly onto the caterpillars' bodies. Be prepared to repeat the process if necessary.
Attract Predators to the Yard That Eat the Caterpillars
The easiest way to control eastern tent caterpillars is to leave the job to predators who eat them. Their main predators are birds; species that will eat them include blue jays, cardinals, red-winged blackbirds, and robins. All you have to do is foster an environment friendly to birds. To do this, grow large shrubs such as lilacs (Syringa spp.) that will furnish cover to wild birds. Birds are less inclined to visit open areas because this exposes them to predators. Provide the birds with water, whether it be with a birdbath or with a water feature. Avoid using harsh chemical herbicides and pesticides, which could harm these birds.
Signs of an Infestation of Eastern Tent Caterpillars
Few insect pests advertise their presence as clearly as eastern tent caterpillars do. After hatching in spring, they create their trademark silky nests in the branch forks of host trees. They sleep in these nests, which afford them protection from bird predators. Even if you miss spotting the tents, you will be alerted to their presence by the loss of foliage in affected trees.
What Causes an Eastern Tent Caterpillar Infestation?
Only certain types of trees serve as hosts to the eastern tent caterpillar. If you do not grow any of these trees, then the pests will not be attracted to your yard. It is mainly trees in the rose family that serve as hosts: apple, cherry, crabapple, hawthorn, peach, and plum trees.
How to Prevent an Eastern Tent Caterpillar Infestation
Preventing an infestation of eastern tent caterpillars begins with understanding their life cycle.
The moths of eastern tent caterpillars lay eggs on the small branches of host trees in summer. But these eggs overwinter on the branches, not hatching until early spring in the following year. When the eastern tent caterpillars emerge, they begin spinning their silky nests in branches not far from where they hatched. The caterpillars eat the most foliage on their host tree in mid-spring. They continue spinning the tents, which can become as long as 1 foot or more.
When the caterpillars have matured, they crawl to the ground, where they make cocoons in sheltered areas. They enter the pupation phase of the life cycle. Adults (moths) emerge in a few weeks and mate. The female lays eggs on host trees in summer, completing the cycle.
Based on awareness of this life cycle, you can easily prevent an infestation of eastern tent caterpillars through pruning. Make it a point to inspect host trees for egg masses when you prune them. Prune off branches that have egg masses attached to them. In addition to the other benefits of pruning, this practice will prevent infestations of eastern tent caterpillars.
Eastern Tent Caterpillar vs. Similar Caterpillars
Unfortunately, there is more than one type of hairy caterpillar that eats the leaves of trees in spring. Here are some identifying features to keep in mind of two others that are problematic in the eastern United States. Learn these features so that you can tell each of the three pests apart from the other two:
- Forest tent caterpillar (Malacosoma disstria): This pest is closely related to the eastern tent caterpillar; both are native to North America. But, despite having "tent" in its name, this pest, unlike the eastern tent caterpillar, does not build silky tents. In fact, the eastern tent caterpillar is the only caterpillar in the region that makes a silk nest in the crotch of a host tree. The two also differ in appearance, if you look closely. While a mature eastern tent caterpillar will have a white stripe running down its back, the back of the forest tent caterpillar is marked with a row of white, keyhole-shaped spots. Hosts for the forest tent caterpillar include such forest trees as aspen, oak, and sugar maple. Like eastern tent caterpillars, they are not a problem for coniferous trees.
- Gypsy moth caterpillar (Lymantria dispar): Unrelated to the tent caterpillars, gypsy moth larvae are an invasive species. During one of the cycles when large infestations of them occur, they are one of the most pernicious pests in the suburbs and forests of eastern North America. Unlike the tent caterpillars, they are a menace to coniferous and non-coniferous trees alike. While oak trees are a favorite host, they also attack such trees as hemlock, spruce, pine, apple, birch, and spruce. You can tell them apart from the tent caterpillars by the spots on their backs. These spots are pairs of raised bumps, forming two rows running down the back. The first three pairs (closest to the head) are blue; the rest are red.
Can eastern tent caterpillars bite or sting?
No, you do not have to worry about touching either the caterpillars, themselves or their silky tents. Eastern tent caterpillars do not sting. Nor is any irritation caused by touching their nests.
Is the eastern tent caterpillar a silkworm?
No. Despite its silky tent, the eastern tent caterpillar is not a silkworm. The famous silkworm (Bombyx mori) feeds on mulberry trees (Morus genus) and produces a valuable silk. The silky tents of the eastern tent caterpillar are entirely worthless.
Do eastern tent caterpillars come back every year?
Probably not. You can expect some garden pests, such as aphids, to be an annual problem. But the areas in the eastern U.S. that experience eastern tent caterpillar infestations usually experience them in cycles. You might have severe infestations for several years in a row, then have no major infestations for a number of years.