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Swarming moth is unwelcome winter guest

The streaks of brown on the side of the house looked like the work of a mudslinging prankster to Kimberly and Richard Casey. But as the Milton couple drew closer, they saw it wasn't mud, but moths, hundreds of them, basking in the floodlights' glow on a cold December night.


"I didn't know where they were coming from or what they were doing," Richard Casey said. "I thought Mother Nature must be screwed up."

For the past few years, a nameless, tiny brown moth has been braving the state's winter weather, cropping up around Thanksgiving and swarming neighborhoods from Cape Cod to Jamaica Plain through early January.

This year, the outbreak has appeared worse than ever: One Milton resident said the insects covered her front porch on Thanksgiving Day, forcing her guests to use the back door.

The short-lived annoyance the moths cause is nothing compared with the devastation they wreak as ravenous caterpillars in the spring when they attack maple and apple trees, as well as blueberry and rose bushes, specialists say.

"The trees can usually withstand one or two years of defoliation in the spring, and they'll come back," said Branch Lane, Milton's tree warden. "But if this kind of outbreak goes on year after year for four or five years, the trees they've infested will die."

But the tables are about to turn on the mystery moth, entomologists say.

After nearly a year of study of the moth, ranging from the moth's markings to its eggs, scientists at the University of Massachusetts and the University of Connecticut identified the moth's genus and species last week, unmasking the insect as operophtera brumata, or the winter moth.

Entomologists from Cornell University independently confirmed the finding.

With the identity established, "there's some good possibilities we can do something about them," said Joseph Elkinton, an entomologist at UMass who identified the fingernail-size moth with fellow scientist David Wagner of UConn. "In the bug world, this is really big," added Deborah Swanson, a Plymouth County horticulturist who has been tracking the moth's progress here.

The moth either migrated to southeastern Massachusetts from Nova Scotia or was brought from Europe, probably with cargo, Elkinton said. It may have arrived a few years ago or as far back as a decade ago.

With no natural predators in the Bay State, the winter moths, which swarm as they mate in December and disappear by early January, began to multiply.

The moth had never been seen in the eastern United States before it was sighted on Cape Cod around 10 years ago, where it began feasting on maple and apple trees, as well as other foliage.

Slowly the moths spread into Plymouth County and across the South Shore, said Swanson, who said she has seen thousands of the insects in her own backyard in Hanson.

Scientists, tree wardens, landscapers, and gardeners had suspected the moth's identity some time ago, but a debate raged over whether the insect was a winter moth or a Bruce Spanworm, a type of canker worm that also flies as late as November.

Without the identity, no one could be sure which pesticide or predator to introduce to stop its proliferation.

Last week, Elkinton and Wagner, of UConn's Department of Ecology and Evolutionary Biology, made a more exact determination based on observations of the female winter moth's wings.

When winter moths began to proliferate in Nova Scotia and the Pacific Northwest, scientists there fought back by introducing a known predator, the tachinid fly, to the area. In short order, the moths virtually disappeared.

State officials, who are aware of the moth's progression in Massachusetts, Elkinton said, could also decide whether some areas will need pesticides to kill the caterpillars once they emerge from the ground in early spring and climb trees to feast.

State forestry officials could not be reached yesterday.

In Milton, Lane said the moth may prove hard to eradicate.

"It's very difficult to have enough predator to take care of the whole problem," he said.

Meanwhile, the nuisance the moths have caused South Shore residents is about to end naturally, at least for now, Elkinton said. The winter moth's mating season should end within a week, when the adult insects lay their eggs and die.

Some residents of the South Shore say the moths have already begun to disappear.

"We've got them all over the garage doors. There's usually 100 of them every night. . . . Oh, wait, they're all gone," said Walter O'Leary, of Milton, when asked about the moths last night. "I wonder where they went."

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