From Hills of Menemsha to Oak Bluffs, Hungry Caterpillars Munch Away Leaves


They're back.

A caterpillar outbreak that left large swaths of trees completely bare of leaves last summer has returned to feast on Vineyard foliage.

Across the Island this weekend millions of tiny green winter moth inchworms - which have been munching away on oak, apple and maple leaves - dangled from branches on silky threads to announce their uninvited arrival.

Infestations were reported from the hills of Menemsha to the highlands of East Chop, where one resident said he needed an umbrella to protect himself from falling frass, a polite name for caterpillar excrement.

"I was walking in the woods yesterday and you could hear the frass. It almost sounded like gentle rain," said Sheriff's Meadow Foundation executive director Dick Johnson. "I think we're about to see the explosion we've all been afraid of."

For months Island arborists have been awaiting the return of the winter moth caterpillars, which some say may be the biggest outbreak of leaf-eating insects since the gypsy moth of the early 1980s.

Originally from Europe, the non-native winter moth has caused widespread defoliation along the Massachusetts coast - covering almost the entire length of Cape Cod and extending as far north as Gloucester. The pests are now well established in the region, where they thrive without natural predators.

Winter moth probably arrived in Massachusetts five years ago, but arborists at first mistook it for the native fall cankerworm. The true culprit - whose latin name is Operophtera brumata - was not identified until December 2003, once the outbreak had gotten out of hand.

A group of University of Massachusetts scientists studying the winter moth population in southeastern Massachusetts estimate that the numbers may already be in the trillions, with even more to come in years ahead.

"It's fair to say that the statewide numbers increased again this year," said University of Massachusetts entomologist Robert Childs. "Requests for treatment have gone up about tenfold in the last year," he added.

In some areas this winter, university researchers counted between 1,000 and 2,000 female moths per tree. Each female lays about 150 eggs, which translates to roughly a quarter-million eggs per tree.

No one knows how the European pest made its way to coastal Massachusetts, though it has been eating leaves in eastern Canada since the 1950s and first appeared in the United States, namely Washington and Oregon, in the 1970s.

Although it can make summer foliage look as barren as winter, the moth earned its name because the adults emerge from cocoons to mate in late November or early December. The moths were as ubiquitous as snow flakes on the Vineyard this winter, often seen flying around outside lamps or holiday lights.

"Coming home down Cedar Tree Neck this winter, I would see dozens and dozens of them," Mr. Johnson recalled. "It looked like it was snowing. I'd never seen anything like them."

The female moths lay eggs on tree trunks, in branches and beneath bark scales and loose lichen. The eggs turn orange and then bright red just before hatching, usually in late April.

The caterpillars then crawl into enclosed leaf buds, where they begin feeding. Experts say that this may have been a particularly damaging spring for the Island trees because the cold weather caused the leaves to bud so late, giving caterpillars extra time at the buffet table.

This weekend much of the canopy in Menemsha looked like swiss cheese.

"We'll get a lot more bud damage with the cooler spring that we had," said arborist Steve Masterson of the Polly Hill Arboretum. "Normally they'll feed until mid-June. But I would add ten days onto that."

Winter moth caterpillars continue to feed once the buds have opened, swinging between branches and trees on silken threads - an act called ballooning. They eat everything from oaks to maples to fruit trees, and have even been known to make their way down to rose bushes.

Once a caterpillar has had its fill, it will slide down a thread and migrate into the soil to spin a cocoon and pupate, only to emerge again as an adult moth around Thanksgiving.

Walking through the woods during caterpillar ballooning is not a pleasant experience. It can feel as though you are walking through a giant spider web, and you may soon find yourself covered in inchworms and frass.

"The walk to Lambert's Cove Beach is nasty," Karin Stanley, outreach coordinator at Polly Hill Arboretum, said yesterday. "They're everywhere. All the leaves were just holes."

Although a summer without leaves does not pose an immediate threat to a tree, those that are defoliated year after year can die within four years. Winter moths in parts of Nova Scotia have been blamed for 40 per cent mortality in the red oak population.

For a defoliated tree, experts recommend watering the entire root structure at least once a week to help prevent lasting damage. Consulting with an arborist is also recommended.

Pesticides and insecticides that can help control the infestations include Bacillus thuringiensis (BT) and spinosad; both are accepted for use by organic growers.

Joseph Elkinton, a forest entomologist and professor at the University of Massachusetts, is raising caterpillar-killing flies in a laboratory at Otis Air Force base in Falmouth. The flies helped control a winter moth outbreak in Nova Scotia years ago, though some scientists worry about introducing another non-native species into the region.

At the West Tisbury selectmen's meeting last week, finance committee member Peter Costas, who also works at Vineyard Gardens, asked selectmen to explore using certain pesticides to protect town trees from the caterpillars.

Selectmen said they were eager to help, although the task at hand appeared more Herculean than the town could afford.

"The problem is," longtime selectman John Early explained, "the infestation is so widespread, we couldn't possibly budget enough."