Winter Moth Mating Season Is Upon Us

December 17, 2015

So many of the things we see all around us this time of year came to us from Europe. Germany gave us the Christmas tree. Holland gave us Santa Claus. And – about 15 years ago – our European brethren gave Eastern New England an unexpected new seasonal tradition that has taken root: The winter moth. We’re at the tail end of their peak mating season right now, and that’s a bigger deal than it might sound like.

Nobody is really quite sure how it got here, but sometime in the late 1990s the winter moth began popping up all across eastern Massachusetts. Then Rhode Island. Then Maine and Connecticut.

"This is not normal. As in they’re an invasive species. They shouldn’t be here," said Nicholas Block, a biology professor at Stonehill College, and something of a winter moth geek. Back home in Europe, this moth has plenty of enemies that keep them in check - some wasps, predatory beetles, shrews. Here? Not so much.

"They’ve kind of exploded along the coast because there’s no natural predators and no natural parasites to knock ’em back so their populations growing at an uncontrolled rate," said Block. 

This might be fine if all they ever did was do what they are doing now. The males flapping about, antenna up. The wingless females poised on tree trunks, releasing pheromones. All of them with one thing on their mind: Mating.

"They are no danger to humans or clothes or anything," explained Block. "If there’s one in your house it’s not gonna do anything other than flutter around and be annoying basically."

“They are voracious,” said Block. “They love maples and oaks. Backyard trees, local forest trees. They’re not very picky and that’s part of the problem.”

In recent years, the moths have defoliated millions of shade trees, killed plenty more, and affected blueberry and cranberry crops all along coastal New England. There’s a cautionary tale here from the 1930s when this same winter moth took root in Nova Scotia and spread its wings. There, some Red Oak forests saw upwards of 40 percent of the trees die. 

"So you’re talking about half the forest dying just simply because of this one little moth," said Block.

While pesticides can be effective on a local scale, Block says a more wholesale solution can be found - not in a bottle - but in nature.

"The best control measure is actually this little fly - a parasitic fly - that lays its eggs on leaves. The caterpillar then eats the leaves and eats the eggs and then the eggs hatch and then eat the caterpillar form the inside out."

A little gross? Sure. Effective. You bet.

The fly efforts are reliant on one lab: Dr. Joseph Elkington at the University of Massachusetts.

“I am the only line of defense in terms of a biological control of winter moth,” Elkington said. “It takes a fairly sizable crew and a sizable effort.”

Professor Elkington knows what you’re probably thinking right about now. And — he says - don’t worry.

"'Well, how about the flies? Are they going to become a problem themselves?' and the answer is no because this fly specializes only on winter moth," said Elkington.

For years, Elkington and his team have been painstakingly gathering fly pupa in Canada, carefully raising them in his lab, and releasing the adult flies in targeted areas.

"We’ve released it at 40 different locations from Maine through Eastern Massachusetts, Rhode Island and Southeast Connecticut and have established it successfully in 17 locations," said ELkington.

The flies have their work cut out for them. A single tree can be infested with 100,000 caterpillars, a single acre with 10 million of them. And as Elkington releases just a couple thousand flies at a time, the process takes time.

"That’s a lot for the fly to cope with it takes several years for the fly to catch up with the much larger population of winter moth," he said.

Elkington is starting to see encouraging results in places like Lexington, Arnold Arboretum and especially Wellesley. Still, he says, this is nature after all and there are no guarantees.

"It remains to be seen whether our efforts will be enough, I’m fairly confident now that we’ll at least get the fly established and then we’ll see whether that’s enough."

This is how the moth was beaten back in Nova Scotia, where it no longer poses a threat. And if Elkington can replicate those results here, we’ll have more to than just our city’s majestic Christmas tree to thank our Canadian friends for this time each year.

Are winter moths buzzing all around the lights on your house? You can help scientists control the winter moth population by taking part in the Massachusetts Introduced Pests Outreach Project's 2015 Winter Moth Survey here.