An Infestation of Caterpillars Gobbles Foliage



Breakfast, lunch and dinner are over - or almost over - and now it's time for a rest.

But the voracious caterpillars have left their mark and in some pockets of the Vineyard this year there is a lot less foliage - or no foliage at all.

"Up-Island is a huge geometrid outbreak that has defoliated large sections of forest at Menemsha Hills. The caterpillars are everywhere - with the sound of their falling frass as one of the loudest sounds, aside from the birds taking full advantage of the leafy carnage," wrote Lloyd Raleigh, the Vineyard entomologist for The Trustees of Reservations, in an e-mail to his colleague Paul Goldstein.

The e-mail was sent two weeks ago.

"There's a caterpillar on the Vineyard and it's going ballistic," Mr. Goldstein confirmed yesterday. A moth expert with long ties to the Vineyard, Mr. Goldstein is assistant curator in the division of insects for the Field Museum of Natural History in Chicago.

"You can walk in the woods and it sounds like it's raining - we've got caterpillars all over the place," said Dick Johnson, executive director of the Sheriff's Meadow Foundation.

Mr. Johnson said he has not seen any large areas of defoliation at the foundation's Cedar Tree Neck Sanctuary, but there are widespread reports of bare trees in other areas, including along the north shore. At Spring Point off North Road in Chilmark, an entire section of trees lining the road is bare. Same story for a swath of oak trees near the Martha's Vineyard Family Campground off the Vineyard Haven-Edgartown Road. In Oak Bluffs a hedge of roses at a private home near the Lagoon has only scant foliage and may not flower this year. In the Lambert's Cove section of West Tisbury a stand of locust trees along the edge of a woodland is nearly bare.


The culprit? Entomologists say in fact there has been an explosion of caterpillars this year, so it's hard to pin down exactly, but the most troubling trend is the East Coast emergence of the winter moth, a new European pest that has no known predators on this continent.

Winter moths first appeared in eastern Canada, and the pest is now showing up in coastal Massachusetts, from the North Shore down to Cape Cod and the Vineyard.

"This year is the first major outbreak in the Eastern United States that we know of and it's significant," said Debra Swanson, extension educator for the Plymouth County/UMass Extension.

There is no longer an extension service on the Vineyard.

Named because it emerges in an adult stage to breed in late November and early December, the moth deposits its eggs on tree trunks, in branches and beneath bark scales and loose lichen. The adult moths die after breeding (females are flightless) and the eggs winter over, hatching when temperatures reach about 55 degrees. During cool springs the eggs may hatch late.

"It has an annoying habit of hatching in late April - this year it was on Patriot's Day," Ms. Swanson said.

The newly hatched caterpillars crawl up trees and produce silken threads which allows them to disperse by "ballooning."

"They come down in silken threads and they will feed on many things," Ms. Swanson said.

Because the caterpillars feed while flower buds are emerging they can cause great damage to fruit crops like apples and blueberries, Ms. Swanson said.

"What happens is when the flower opens it opens in tatters and there is nothing for the bees to pollinate," she also said.

The caterpillar's appetite is widely varied and includes oak, ash, birch and roses, among others, Ms. Swanson said.


Mr. Raleigh, a respected local entomologist, was out in the field and could not be reached for comment at press time. But in his e-mail to Mr. Goldstein he reported his own observations about the preferred food for this new caterpillar.

"They're feeding on oaks, but not exclusively - also shadbush, arrow-wood and some huckleberry," he wrote. "They are adverse to maples and sweet pepperbush, among other lowland plants."

Ms. Swanson said there has been some confusion about the identity of the caterpillar, partly because the winter moth is similar to the fall canker worm, a more common caterpillar which is native.

Both caterpillars are inch worms, also known as loopers, and they have similar coloring. The winter moth caterpillar is smooth-skinned and gray or light green with a subtle longitudinal stripe running down its side.

The fall canker worm has also been active this year, Mr. Goldstein said, and he said it is unusual to see the explosion of two caterpillar populations in the same year.

"It's kind of odd that it's happening simultaneously - what's going on to cause this kind of outbreak?" he said.

The caterpillars can be controlled by using BT (bacillus thuringiensis), a bacterium that is specific to the caterpillars of butterflies and moths. A biological insecticide named spinosad is also effective. BT and spinosad are accepted for use by organic growers. But Ms. Swanson said control is no longer an issue for this year because the caterpillar has now pupated in most areas. The caterpillar pupates into the soil, where it will remain until late fall when the moths emerge.

Ms. Swanson said late November and early December is the time when Vineyard residents should be on the lookout for clouds of moths. The moths are often attracted to holiday lights.

Meanwhile, trees and shrubs that have been defoliated by the moths can be under extreme stress, and Ms. Swanson said the best antidote is simple and comes straight from the garden hose. "Water. Trees and shrubs should get ample water - it's the best defense, the best thing people can do for them," she said.


One experienced arborist has this prescription for newly planted trees and shrubs: Water once a day for a week, once a week for a month and once a month for a year.

The emergence of the winter moth on the Vineyard puts the spotlight on the complex relationship between science and nature. Ms. Swanson said a three-year study is now under way at the University of Massachusetts that will examine possible predators for the moth, including parasitic flies and wasps.

Mr. Goldstein, who has done scientific work on the Vineyard for more than 20 years, said he is familiar with the UMass study. He praised the credentials of the entomologists conducting it, noting that the study is examining the use of a host-specific parasite for possible control of the moths. But he also said that such experiments require a good dose of caution. An experiment on the Vineyard that introduced a parasitic fly to control the gypsy moth a few years ago is now suspected in the decline of the imperial moth, a giant silk moth which is now endangered. Mr. Goldstein said the Vineyard is the last place in New England where there is still an imperial moth population.

"The Vineyard has the highest concentration of threatened invertebrates of anywhere. There is a parallel here to the outbreak of this exotic guy - I am always cautious about introducing alien species to control another alien," he said.