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Gyspy moths emerge in May: Here's what you need to know

Last year, gypsy moths ravaged trees across Massachusetts. The pests are about to emerge, but their population has dwindled, experts say.

May is finally bringing some warmer weather to Massachusetts, but it also brings some annoyances like gypsy moths, an invasive species that damage trees all across the commonwealth.

Gypsy moths begin to emerge as caterpillars in May, and in past years these pests have ravaged Massachusetts trees. In 2017, more than 920,000 acres of forest were defoliated by gypsy moths.

This year, though, trees might see some reprieve.

“We’re expecting the gypsy moths population to be quite a bit lower than they have been over the past few years,” said Ken Gooch, forest health program director for the Massachusetts Department of Conservation and Recreation. “The population got hit pretty hard by a fungus, Entomophaga maimaiga, last year, that really wiped out quite a bit of the numbers.”

That fungus, Gooch explained, is soil-borne, and last year’s cool and wet spring caused it to spread, thus harming the gypsy moth populations.

In past years during the drought, when soil across the state stayed dry throughout the spring, that fungus wasn’t able to grow, and so the pest population wasn’t kept in check.

That fungus is everywhere though, Gooch said, some trees will still be affected. And since gypsy moths are “very, very voracious feeders,” said Kevin Narbonne, an arborist with the Hartney Greymont tree and landscape company in Needham, their damage could be significant.

Narbonne explained the danger of these pests with a metaphor: Trees have energy reserves, like how you have a savings account. If you keep withdrawing money, you won’t be able to pay your bills. When gypsy moths feed on a tree, it taps into those reserves, like you spending money you don’t have.

“Eventually, if a tree gets defoliated and defoliated,” he said, “like that draining of that savings account, that can send a tree into a downward spiral.”

There’s a lot of reasons you want to keep your trees healthy, Narbonne said. They can reduce the amount of stormwater that collects on your property, help with erosion control, lower the amount you spend on heating and cooling your home, and of course, add aesthetic appeal and sentimental value.

If a healthy tree is defoliated by gypsy moths three years in a row though, Gooch noted, that can be detrimental to its survival. There are preventative options, Narbonne noted, to keep gypsy moths from eating your trees, and the time to be preventative is now. But he knows that may not be feasible for everyone.

“In a perfect world, we’d have you treat every tree, but the world is not perfect and budgets are a constraint,” he said. “It’s good to have someone [at least] look at your trees, especially if they hold significance for you.”

Gypsy moth facts

The gypsy moth was introduced to Massachusetts in 1869
They spread to every city and town in Massachusetts by 1922 and remain “a major threat to forest health” here, state officials say
In 2017, a severe gypsy moth population caused more than  923,000 acres of damage in Massachusetts
The small caterpillars will emerge in May and adult moths emerge in mid-July