Caterpillars Chew Up Acres of Trees

Thousands of acres of trees in three counties in New York have been defoliated by a population explosion of forest tent caterpillars, which have left normally green hillsides marred by long tracts of brown, barren foliage.

The caterpillars, which are the larva stage of a small, buff-colored moth, have stopped feeding, and begun spinning cocoons in leaves and bark. However, at the height of the infestation, witnesses said, it was possible to hear the sound of their droppings falling from trees.

"It sounds just like it's sleeting," says Dan Palm of Hobart, N.Y., a landowner and former director of the New York State Forest Owners Association. "You can actually hear them chomping and chewing away. It's eerie."

At their height, the caterpillars, sometimes called armyworms because they travel en masse looking for food, swarmed the exterior of houses and cars in the most affected areas of Delaware, Schoharie and Green counties.

"They would climb up anything," says Astrid Nilssen, an East Meredith homeowner, who used brooms and a vacuum to remove caterpillars that were scaling the exterior walls of a neighbor's house. The homeowners were in New York City when the caterpillars were at their peak.

Nilssen also helped a friend who is a landscaper protect valuable shrubs by digging moats around bushes and trees and filling them with soapy water that drowned encroaching caterpillars by the thousands. The moats soon filled and had to be cleaned out, she says.

"One time I scooped three buckets of dead caterpillars out of one moat," Nilssen says.

The defoliation is so widespread that the state Department of Environmental Conservation plans to make a flyover to assess the damage, which encompasses "tens of thousands to hundreds of thousands of acres," says Peter Innes, natural resources supervisor for the DEC. "We're coordinating with the aviation unit of the state police to do aerial detection flights."

The forest tent caterpillar is similar to but different from the Eastern tent caterpillar, which leaves cocoons in the crotches of fruit trees. It can be identified by a series of light spots on its back that resemble a keyhole. Both a mild winter and what appears to be a natural 15-year cyclical boom in the caterpillar population appear to be factors in the recent boom, the likes of which haven't been seen since the early 1980s, Innes says.

The loss of leaves puts stress on trees, but most will recover and produce more leaves if the tree is not compromised by other environmental factors. One upside to an oppressively wet June is that defoliated trees are getting the moisture they need to re-leaf, said Palm, who is the chairman of the Forestry Committee of the Watershed Agricultural Council.

"There's so much moisture, the trees don't have the stress from dryness," he says.

When the trees re-leaf, Innes explains, "the leaves won't be as large and won't produce as much chlorophyll as they normally would." The sugar maples have been most affected, since they are a favorite of the caterpillar, but other trees were stripped as well as by the hungry herbivores. Palm says he has a friend who has an entire oak grove stripped bare of leaves.

"They like maples," Palm says. "But they'll eat pretty much anything in their way."

Their numbers were so great that many of the caterpillars simply starved to death, Innes says. "The population gets so high, it just collapses," he said.

One of the beneficiaries of the boundless supply of moths in the making is a type of fly, sarcophaga aldrichi, whose maggots feed on the pupae of the caterpillar.

The large gray flies have been so numerous that rumors have spread that the DEC released them. "We didn't release them. It's the result of a normal predator-prey relationship," Innes says.

There is some concern the caterpillars may have one more shot at forests and yards.

"If conditions are right, they can lay eggs and hatch before the first frost comes," Palm says.