BAR HARBOR — The white plastic canister hanging from a low branch of a tree near the fountain in the Village Green here looks, at first glance, like a bird feeder, but it’s there to capture winter moths.
It’s part of a Maine Forest Service project to chart the spread of the insects that, as caterpillars in the spring, devour the tender leaves and buds of oak, maple, apple and other hardwood trees.
The winter moth is an invasive species that was introduced to Nova Scotia from Europe in the 1930s and now has spread to several New England states.
The males of the species can fly, but the females don’t have wings. They crawl up the trunks of trees between early November and late January.
“The males will find the females on the tree trunk, where they will mate, and then the females crawl up the trunk and lay eggs on the branch tips,” said Tom Schmeelk, a Maine Forest Service entomologist.
“Usually in early April, the eggs hatch and the caterpillars come out and start mining the leaves and the buds before the buds open. They will continue to feed and basically defoliate the trees.”
Severe defoliation over three or four years can kill a tree.
Around the end of May, when the green, inch-long caterpillars are fully grown, they drop off the tree and go into the soil to pupate. They emerge six or seven months later as moths.
Over the past few years, winter moths have been found along the Maine coast from Kittery to Mount Desert Island. So far, the greatest loss of trees has been in the greater Portland area, particularly in Cape Elizabeth.
Chemical sprays have been used to control winter moths. But Schmeelk said the two most effective and environmentally safe methods are “banding” trees and releasing a type of fly that preys on the moths.
With “banding,” a sticky tape a few inches wide is wrapped around a tree trunk to capture female moths as they try to crawl up the tree to lay eggs.
In the past few years, thousands of moth-eating flies have been released by the Forest Service in Maine communities, primarily along the southern coast
“We’ve had pretty good success with that in a lot of places,” Schmeelk said.
This year, he said, the Forest Service has placed about 70 winter moth traps in coastal communities from Bar Harbor to Kittery.
“It’s a monitoring tool to see where the moth is and in what concentration,” Schmeelk said. “If we see that the concentration in a given town is higher this year than last year, we’ll update our risk map for defoliation.”
The hanging traps capture only male moths because the females can’t fly. Inside each trap is a rubber lure impregnated with a sex pheromone, a chemical given off by female winter moths to attract males.