Eastern Tent Caterpillar: Problem in the Woods?

Joshua VanBrakle Monday, 29 May 2017

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Earlier this spring I was driving down I-81 to visit family. As I drove through the woods in Pennsylvania, I noticed a ton of tent caterpillars. Their white tents were noticeable even at 65 MPH.

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Eastern tent caterpillars are native to North America. Odds are you’ve seen their characteristic tents like the one above in your trees from time to time. They especially enjoy cherry and apple trees, but you can also find them on maples, hawthorns, and some other species.

A lot of landowners get concerned when they see these tents on their trees. Are their trees doomed?

In general, no. Eastern tent caterpillar, along with another tent-building moth, the fall webworm, rarely cause permanent damage to healthy trees. The tents might look ugly, but they aren’t hurting your trees.

I’ve seen people come up with some interesting (scary?) ways of dealing with these tents. Chemical insecticide is a common method, as is fire. Something about these tents brings out people’s inner pyro. I know one homeowner who attached a stuck-open lighter to a long pole so he could reach the tents and burn them.

By the way, that’s an example of what not to do. You’ll do more damage to the tree by burning it or potentially starting a fire than the insects are doing. Never use fire to control eastern tent caterpillar.

In fact, it isn’t necessary for you to “control” eastern tent caterpillar or fall webworm at all. In the woods, leave them alone. Your trees will be fine. In your yard where aesthetics are more of a concern, you can manually knock down tents or prune off the branch they’re attached to. Skip the insecticide. And unless the tent really bothers you, it’s fine to leave it in place even in a yard tree. The caterpillars will help attract songbirds like cuckoos, orioles, chickadees, and nuthatches, which all like to eat them.

That said, some caterpillars can damage or even kill your trees, including one closely related to eastern tent: the forest tent caterpillar. But contrary to their name, forest tent caterpillars don’t build tents, so you’re still safe leaving the tents intact.

Your best defense against insect pests in general is to make sure the trees in your woods are as healthy as they can be. That means they should get plenty of sun, water, and nutrients to grow big, healthy crowns of leaves. If your woods are crowded with trees tightly packed against each other, no one tree will have much in the way of reserves to protect itself from pests like forest tent caterpillar. If the trees have more room to grow, they’ll be in a better position to survive an attack.

One way to get this extra room is to do a thinning, or woodlot improvement harvest. This operation removes smaller, unhealthy trees that are competing with the larger, healthier ones. Before getting started with one of these cuts, it’s a good idea to contact a professional forester for advice first.

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