Hungry, Hungry Caterpillars Decimate Trees in New England

A gypsy moth caterpillar chomps through leaves, sometimes leaving huge holes, sometimes eating everything that's green. Phil Burt/

It's not pleasant to sit in your backyard and watch legions of caterpillars inch their way up your house, around your deck and down your fence, chomping through leaves and decimating your trees.

But that's the scene in many places throughout New England, as European gypsy moth caterpillars have been eating their way through foliage since they hatched in early May. The unofficial guess is they number in the millions as they've overtaken trees (and yards) as part of what may be the worst outbreak in more than two decades. In 1981, about 1.5 million acres in Connecticut were defoliated by the destructive caterpillars.

Depending on the degree of infestation, tree damage can range from light to total defoliation. The caterpillars feed primarily at night and go through several growth stages, or instars. As they grow, they consume more and more leaves. As the growth cycle winds down in late June, trees can look as if they've been defoliated overnight, according to the Wisconsin Department of Natural Resources.

The gypsy moth was accidentally introduced into New England in the 1860s by an entomologist in Massachusetts who had some sort of silk-making scheme, according to this National Park Service. Since then, the moths and related caterpillars have become a problem through much of the Northeast and parts of the Midwest. Typically, their numbers are controlled naturally by the gypsy month fungus, but the fungus doesn't spread easily during dry conditions. Last year's drought-like weather in parts of Connecticut and Massachusetts meant the gypsy moth caterpillar population skyrocketed, says Dr. Kirby Stafford, chief scientist and state entomologist at the Connecticut Agricultural Experiment Station.

"For a lot of residents that are getting heavily hit, it's overwhelming," he says. "[The caterpillars] are crawling all over the house, the trees, the deck. You can hear them munching and eating and there's steady sound of frass — the caterpillar poop — dropping."

gypsy moth caterpillar poop
After they eat, this is the aftermath of all those gypsy moth caterpillars. Phil Burt/

The caterpillars prefer to eat oaks and have been known to strip those trees bare, says Stafford, but this year they can't be such picky eaters.

"We know the caterpillars are hungry if they're switching over to pines and spruce," he says. "There are so many of them, they'll start moving to other things once they strip the vegetation off the trees."

Healthy oak trees can often recover from partial or even one complete defoliation, says Stafford, but some conifers are not so lucky. Those trees often die.

"With these caterpillars, we often face the prospect of tree mortality," Stafford says.

Some of the caterpillars have started to enter their next stage, pupae, which means millions of moths will soon be flying around.

"Then you will have moths everywhere and the egg masses everywhere ... on fences, on furniture, on houses, on the trees," says Stafford. "But at least that will kind of give us a feeling of what we'll be facing next year."