Moth outbreak plagues our forests


NUMEROUS LYMANTRIA DISPAR DISPAR (aka the gypsy moth) attack a tree in the Monkton woods last week. The exotic invasive species feeds on tree leaves and can defoliate entire forests. Most trees will survive the outbreak and grow a second set of leaves this summer, but those already suffering from environmental stress may die. Independent photo/William Haig

A LONE LDD caterpillar crawls across a leaf in the Little Hogback Community Forest in Monkton on Friday. It is joined by millions more just like it, which together have defoliated entire sections of this forest. Vermont is experiencing an outbreak of the invasive species, its first since 1991. Independent photo/William Haig

AN UNPLEASANT THING about LDD caterpillars, aside from the fact that during outbreaks they strip entire forests of their leaves, is the product of their constant eating: “frass” (feces). At the height of an LDD outbreak, millions of caterpillars will produce a constant rain of tiny brown pellets, producing a steady pelting background noise throughout the forest. Independent photo/William Haig
Trees already have plenty on their plate. Unlike birds that can fly away, trees have to stand there and take it. — David Brynn

MONKTON — There’s a spot in Monkton’s Little Hogback Community Forest, about a quarter-mile up a logging trail, that last Friday felt like a dividing line between spring and fall.

Downhill from the trail, maple, young ash and other trees provided the cool green shade typical of a Vermont June in the forest. Uphill, in a drier microclimate populated with oaks, beech and hardhack, it looked like November. Dead leaves on the ground, the sky visible through the branches. Gray and dreary.

And then there was the sound. Like a gentle rain. Or morning dew dripping on your tent. But this was not water pelting the ground. It was the frass (feces) of millions of caterpillars eating their way through stands of oak and other trees on their preferred menu. As they munched their way from tree to tree in hairy, sticky, writhing masses, tiny brown pellets of frass bounced off tree branches, forest litter and a reporter’s notebook below.

Vermont is in the midst of an outbreak of Lymantria dispar dispar (LDD), also known by the unfortunate moniker “gypsy moth.”

“This is a pretty significant outbreak,” said David Brynn, executive director of Vermont Family Forests, who gave the Independent a guided tour of the forest. “They’re part of our ecology, but other species tend to keep it in check. Every once in a while they break out into a feeding frenzy.”

As Brynn spoke a broad-wing hawk flew overhead. With the tree canopy devastated it had a clear view of the forest floor.

The invasive LDD arrived in this country more than a century ago and made its way into Vermont around 1965. The last major outbreak of LDD occurred in 1991.

The caterpillars prefer oak, but they’ll eat pretty much anything — maple, pine — once their populations reach a certain size.

We’re nearing the peak of forest destruction in this particular outbreak, Brynn said.

Once the caterpillars have moved on, the trees will immediately attempt to put out a whole new set of leaves, which will be smaller and misshapen. It’s a difficult thing for even healthy trees to do in one season, and on a short timeline.

Some trees that had already been under heavy stress, whether from drought or other environmental conditions, may die, Brynn said. Most will suffer from “dieback,” losing the outer reaches of their branches and shrinking in size.

But in the long run they will recover.

“The good news is that the forest is resilient,” Brynn said.

But such events should awaken in us a heightened awareness of the stressors, including invasive species, of a rapidly changing climate.

“Trees already have plenty on their plate,” Brynn said. “Unlike birds that can fly away, trees have to stand there and take it.”

For more information about LDD, see the Vermont Agency of Agriculture’s gypsy moth explainer online at tinyurl.com/jrba9ksx.

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