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Spongy moth caterpillars start seasonal snack

A spongy moth caterpillar on a backyard shed
Lucas Willard
A spongy moth caterpillar on a backyard shed

A common backyard pest has returned, as some parts of the region are reporting sightings of a seasonal nuisance.

You might have seen them crawling up the trees in your backyard or maybe on your Adirondack chair. Spongy moth caterpillars, identifiable by their dark, hairy bodies and blue and red spots, are here.

Rob Cole, a New York State Department of Environmental Conservation forester, said sightings this spring are part of a lingering population explosion that defoliated parts the Northeast.

“This outbreak started several years ago now out in the Finger Lakes and has moved around the state and the entire 87 corridor has been impacted,” said Cole. “But the northern areas, up in the eastern Adirondacks, the populations have really crashed up there. And so, the worst of it is going to be south of Albany.”

In the summer of 2021, trees across large portions of the Northeast saw their leaves eaten away by the larval army.

But while the spongy moth caterpillar has been spotted in areas like the Hudson Valley in recent weeks, it doesn’t mean the larvae will have a repeat performance of three years ago.

Arborist Fred Breglia of the Landis Arboretum in Esperance, New York, did not notice as many of the spongy moth’s tell-tale egg cases earlier in the season.

“The fact that ’21 I think was as bad and, now we're at three years later, and the amount of egg cases I've seen just being out in the woods doesn't seem to be quite even close to the level of what I've seen in ’21, at least around our area. So, I'm thinking it won't be as bad as what we've seen. But you know, we're certainly looking to see some damage,” said Breglia.

The spongy moth has been established as an invasive species in North America since the 19th Century. While it isn’t venomous, officials ask people to avoid touching it and take precautions if working outside – the caterpillar’s hairs can cause skin irritation.

The caterpillar can also be confused with other species, says Breglia.

“So, there's a spring tent caterpillar that attacks fruit trees and other ornamentals. There's also a forest tent caterpillar. And that one, instead of making what I say is a tent for the whole colony, the whole camp, like the spring tent caterpillar, it's much more like the spongy moth in the sense that it sets up its individual little pup tent for itself. And those forest tent caterpillars do not feed on fruit trees and they will feed on the same exact trees that the spongy moth would, like oaks and maples and things like that,” said Breglia.

A few bird and some rodents species will eat the non-native caterpillar, but it’s typically not enough to control an outbreak.

Parasites and fungus will help control populations, especially in wet weather. That’s according to Dale Ila Riggs, owner of the Berry Patch in Stephentown.

“Part of it depends what the spring weather is like, because there is a naturally occurring fungus that will kill them. So, if we wind up with a rainy May, there's a chance that the naturally occurring fungus will take care of a lot of them,” said Riggs.

Forests will bounce back from a defoliation event caused by the caterpillars by mid-summer, though individual trees can be weakened by such happenings.

Rob Cole says homeowners can take some precautions to prevent their favorite trees from being snacked on.

“For the homeowner with few trees in their yard, we do recommend the banding with sticky tape to catch the caterpillars as they walk up and down the trees,” said Cole. “And then later in the season, we recommend using burlap on the trees because the caterpillars, later in June, they're actually looking for a place to pupate, and they'll crawl up in that burlap and put their pupil chambers there, in which case people can go scrape them off and get rid of them.”

Lucas Willard is a news reporter and host at WAMC Northeast Public Radio, which he joined in 2011. He produces and hosts The Best of Our Knowledge and WAMC Listening Party.