What is this strange webbing?

There is this strange sort of webbing on many of the trees at my cottage in late summer and fall. It seems to happen to the same kinds of trees every year around this time. What is this, and why is it happening?
—Lindsey Gottlieb, Lake Vernon, Ont.

Cottage Life’s editors were certain that this “webbing” came from eastern tent caterpillars…until the experts reminded us not to quit our day jobs. In fact, it’s much more likely from fall webworm (another type of caterpillar). “They’re the most common late-summer web makers on a wide variety of broad-leaved trees,” says Kathryn Nystrom, an insect identification officer with the Great Lakes Forestry Centre. The larvae start building the communal nest as soon 
as they hatch in the summer. They use 
it for protection from predators and 
bad weather while they live in the tree and eat the leaves. The webs seem to appear almost out of nowhere, because they start out tiny and people don’t 
usually notice them right away, says Nystrom. “Then, all of a sudden, wham, the tree is covered.”

Generally, the larvae don’t cause much damage, other than defoliation, because they’re late-season insects, explains Mike Francis, a forest health technical specialist with the Ontario Ministry 
of Natural Resources. By the time they attack, the tree has already gathered 
its necessary nutrients and is preparing for winter. “The tree is close to natural leaf-drop anyway,” says Francis. “A 
webworm infestation has very little effect on the tree.”

That said, it might have an effect 
on you: “The nest is kind of unsightly,” admits Nystrom. Sometimes, nests 
can get so large that they surround the entire tree in a creepy, science-fiction-movie kind of way. Plus, trees that have experienced stress—such as disease or drought—earlier in the summer could suffer. “If it’s your favourite tree, you’re going to want to do something about it.” She recommends that cottagers remove the nests when they first start to form.

Once the nests are empty, in the fall, destroying them won’t help the tree (although, if you’re the type to hold a grudge, it may make you feel better—like getting back at those kids who TP’d your house on Halloween). The larvae pupate in the ground over winter; then, in the spring, they turn into moths and get on with the rest of their lives: seeking mates, laying eggs, and fluttering incessantly against light fixtures.