BOSTON (AP) – Deborah Swanson knew there could be trouble this spring when she looked outside her Hanson home in late fall and saw what she described as a “blizzard,” not of snow, but tiny moths swarming to mate.
The moths gathered so thickly around trees where they found females that the bark seemed covered in fur, said Swanson, a horticulturist at UMass Extension in Plymouth County.
Now, the eggs have hatched, tiny worms are devouring leaves around the region and Swanson says it could get ugly.
The culprits are one or more of three similar, voracious moth species, including a European winter moth that’s never been seen in the eastern United States, said University of Massachusetts entomologist Robert Childs.
Researchers still trying to determine if the European moth has actually invaded the state, but said leaves are equally threatened by each species, Childs said.
“They will cause a defoliation if something isn’t done about them,” he said.
The heaviest concentration of worms is in Plymouth County, but Childs said they’re hitting coastal towns from the North Shore to Cape Cod, and could move westward.
Childs said native Fall Cankerworms and Bruce Spanworms are suspected along with the European winter moth. Long term, the European winter moth presents the greater threat to trees because of a lack of natural predators, such as certain fungi and parasites, to keep it in check, he said.
The winter moth is also more likely to move westward because in Europe it’s proven it can thrive inland, while the two native moths have always stayed closer to the state’s coast, where the ocean moderates the climate, Childs said.
The three moth species, all of them green and an inch long when full grown, eat leaves on maples, apples trees, and crabapple trees. The also eat buds on flowering plants, such as blueberries, and feast on various perennials if their primary food sources get scarce, Swanson said.
The cankerworms and spanworms have been defoliating trees in coastal communities for the last several years, Childs said, but researchers expected the problem to abate because the worms were due for a population decrease as part of their natural cycle.
When it was clear the worms weren’t going away, they began to suspect the European winter moth had been introduced, Childs said. Eggs and larvae samples are still being studied, he said.
Swanson said the problem isn’t just that the worms appear to be increasing – she sampled one tree in Abington and found 40 caterpillars on just three leaves. But year after year of defoliation increases stress on trees, causing long-term damage, she said.
The worms are growing and becoming easier to spot. Swanson said homeowners can use bacteria-based pesticides that are effective at early stages, when the worms are easier to kill, and relatively environmentally friendly.
Meanwhile, Wellesley town horticulturist Cricket Vlass said the possible winter moth invasion has made her particularly vigilant, though her town isn’t in the most affected area. She called Childs this week to discuss worms she spotted, which she now believes are the native cankerworms, not the winter moth.
“I’m definitely very nervous about it,” she said. “I lived through the horrible gypsy moth infestation. When (Childs) is concerned, I’m concerned.”
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