While a PhD candidate at Dartmouth College, Justin Richardson does worm research on Vermont's Mount Mansfield in Aug. 2012. Richardson currently works as an assistant professor at the University of Massachusetts Amherst. (Courtesy Justin Richardson)

The Asian jumping worm -- sometimes referred to as a snake worm -- poses a threat to the forest, particularly maple trees, because they eat leaf litter and their castings are not very good for the soil. (UW–Madison Arboretum - Susan Day)

Researchers say that when it comes to invasive earthworms, a particularly nasty annelid species poses a growing threat to a large chunk of New England’s forest ecosystem, including sugar maples.

Crazy snake worms, an Asian invasive prized by fishermen for their aggressive wriggling, first came to the attention of Justin Richardson in 2011, when he began working on a doctorate at Dartmouth College.

Richardson, currently an assistant professor at the University of Massachusetts Amherst, has fond memories of the field and lab work he used to fuel his dissertation — working with Dartmouth Professor Andrew Friedland, he’d visit locations such as the Montshire Museum in Norwich and use a spade to dig up worms from the black, spongy “organic hemic horizon” that lies just beneath the leaf litter in a healthy forest.

After each worm safari, Richardson popped some of his squirming captives into an “acid worm stew,” using a mass spectrometer to tease out how much gasoline-produced lead had accumulated in their bodies. Others he freeze-dried and ground into tiny pieces, which he then incinerated. The ash and fumes yielded up data on levels of mercury, which enters the ecosystem by way of coal-burning plants in places like Ohio.

Richardson’s work showed the worms, also called Asian jumping worms, store large amounts of both lead and mercury in their bodies.

The worms ingest the heavy metals as they gobble up organic material; they then pass the metals up the food chain to predators like red-backed salamanders, robins and the Bicknell’s thrush, which is listed as a species of special concern by the Vermont Fish & Wildlife Department.

Depleting the Forest

The snake worms’ capacity to activate buried heavy metals is just the tip of the iceberg.

The much bigger problem, according to Josef Gorres, a University of Vermont professor and Vermont’s leading snake worm authority, is that the fast-breeding, voracious worms are eating the entire organic hemic horizon in some forests, which has dramatic impacts on the local ecosystem.

“Sometimes, if you go hiking, you go up that hill and look left and right and there’s a lush understory. You can hardly walk through because there’s so much vegetation there,” he said. “When you walk through a forest invaded by earthworms, then you’ll see very little understory. … It’s a really huge difference.”

Here’s why: Unlike European earthworms, snake worms produce castings that are granular, like coarsely ground coffee.

The organic hemic horizon contains about 20 percent organic material. The snake worm’s castings bind up those nutrients in mineral form, reducing the overall organic profile to as low as 10 percent.

Richardson is about to publish a paper examining the impact of the crazy worm on sugar maple seedlings and two other plant species — the Christmas fern, so named for its capacity to remain green into the holiday season, and false Solomon seal, a common native forest plant with white flowers.

The fern, which is good at tapping nutrients from deeper minerals, did just fine in snake worm-heavy areas, but false Solomon seal and sugar maple, which rely almost entirely on the organic material for their nutrients, suffered.

Gorres says the worms are directly responsible for reducing the understory by 50 or 60 percent. Grazers like deer take what’s left, leaving behind only a few inedible species, like Jack in the pulpit.

“If deer come through and see nothing but sugar maple saplings because everything else is gone, that’s what they eat,” Gorres said.

Though many say the early bird gets the worm, an environmental cascading effect triggers what Gorres calls “early worm’s revenge.”

The elimination of a forest understory leaves little or no cover for ground-nesting birds, such as the Eastern whip-poor-will and the common nighthawk, leaving the calorie-laden eggs of those species vulnerable to predation.

Green Thumbs

Worms aerate and churn the soil, which helps gardeners.

“They increase filtration so that means the soil can store more water,” Gorres said. “There’s good reasons why gardeners like them.”

But gardening’s dirty little secret is that the same worms that help bring in a bumper crop of tomatoes might wreak havoc on neighboring woodlands.

In fact, none of the Upper Valley’s earthworms are from around here — the last ice age scrubbed the region free of worms, and they only reappeared after hitching a ride in the soil-packed ballast in European ships.

Asian jumping worms were first identified in the country in 1937, and have since been documented throughout New England.

Snake worms can spread on their own — they wiggle a little deeper into the woods each year — but, like so many invasive species, their travel plans get turbo-charged by human intervention.

Every time compost is transported, there’s a good chance of some worm passengers coming along for the ride.

“Every week, I get three or four emails from people saying, ‘I’ve got these at my nursery.’ Connecticut is totally riddled with them,” Gorres said.

In one typical call Gorres fielded last November, a woman said that soon after buying bagged compost from a large commercial supplier, she’d noticed scads of snake worms in her home garden. She wasn’t sure the compost was the culprit until she opened a sealed, unused bag and found the worms in there, too.

If there’s one silver lining in the spread of snake worms, it’s that public awareness is growing.

Gorres did a survey of master gardeners which found 25 percent — representing nearly every county in the Twin States — had knowingly seen snake worms locally.

Kelsey Haigh, a landscape designer for the White River Junction-based Henderson’s Tree and Garden Services, has definitely seen them.

“They can just eat the mulch in a season,” he said. “You put three inches down and they might eat the whole thing.”

Haigh said worm education is part of the training of the two crews that do landscape maintenance on 20 properties in the area.

“We’ll try not to throw them in the woods,” Haigh said. “Eventually they’ll get there anyway, but we’ll try to keep them in the garden areas. So we’re not dumping in the woods or even close to the woods.”

And Nina Klinck, the designated nursery manager at E.C. Brown’s Nursery in Thetford, said she’s spied what she thinks are snake worms off and on since she started working there in 1995. The worms look like nightcrawlers, but she identifies them primarily by their hard castings, and the speed with which they cover ground.

“They run off like snakes,” Klinck said. “They’re wicked fast.”

But Klinck and Haigh both said that it’s important to keep the presence of the worm in perspective.

“My take on it is, it’s here and the world is always changing and there’s some battles you can’t take on,” Haigh said. “It’s so big, I don’t know how to stop it. So how do we live with it?”

Gorres said that with Vermont’s universal recycling law, Act 148, moving toward mandatory composting for all residents, the potential for the spread of the worms, and other invasives, will grow.

“I support the law absolutely,” he said, “but I hope they address this concern.”

Seeking Pixie Dust

Short of using poisons that would kill a lot more than worms, there’s no effective way to eradicate snake worm populations. A graduate student in Gorres’ lab has identified a worm-killing fungus, and a bacteria, but there’s no clear path to apply that knowledge to practical worm management.

A research lab in Wisconsin found that worms, whether in egg or adult form, can’t tolerate the hottest composting temperatures of above 105 degrees, but that’s of limited use because the adults can simply migrate to the cooler edges of the compost heap.

In order to develop controls, more research needs to be done. And amid the cacophony of pressing environmental research needs, Gorres said it’s been extremely difficult to find grant funding to support his work.

Still, this summer, he said, he’s scraped together enough to explore a promising solution — certain types of sand have granules that are so sharp and angular that, once eaten, slice right through a worm’s guts.

A simple soil amendment “would be a perfect way of doing this in the nursery, to find a magic substance that you can put in the soil, a pixie dust that kills the worms.”

In the meantime, Gorres recommends New Englanders slow the spread by crafting forest management plans that minimize exposure, eliminating fishing bait refuse, limiting the movement of horticultural materials, and inspecting all nursery plants for signs of the worm before planting.

Matt Hongoltz-Hetling can be reached at mhonghet@vnews.com or 603-727-3211.

Clarification

Andrew Friedland is the Richard and Jane Pearl Professor in Environmental Studies at Dartmouth College and also serves as an adjunct professor of earth sciences. An earlier version of this story gave an incomplete title for Friedland.