That’s no regular earthworm: Invasive jumping worms take hold in Vermont

August 12, 2022  |  By Lauren Milideo  |  Correspondent 

Jumping worms (left) resemble the common earthworm (right) although the jumping worm has a ring of light-colored tissue that's flat and completely encircles its body. Photos courtesy VtInvasives.org

As Vermont’s gardens burst with summer’s bounty, gardeners are also eyeing what’s happening underfoot. Healthy soil is always a concern, but invasive worms have been spotted in local plots, sparking worry among growers.

Two types of invasive worms have appeared in Vermont in recent years: jumping worms and hammerhead worms. 

Jumping worms are similar to nightcrawlers, according to University of Vermont College of Agriculture and Life Sciences Associate Professor Josef Görres. Genetic study, he said, indicates that Vermont has three species, all originating in Japan and Korea. The smallest are 1 to 3 three inches long; the largest, up to 8 inches.

The jumping worms have appeared “pretty much all around Vermont except for maybe the Northeast Kingdom,” Görres said. “They're pretty much everywhere and we find them… in many, many gardens, and they are likely in quite a few nurseries as well.” 

Jumping worms are similar-looking to the average earthworm or night crawler, but there are differences to tell them apart. According to the Vermont Invasives website managed by the UVM Extension Service, they are generally smooth and glossy dark gray/brown in color. Unlike a regular earthworm, the clitellum – or ring of lighter-colored tissue around the body near the head – is cloudy-white to gray and it completely encircles the body. Its surface also is smooth and flush with the rest of the body.

Most notably, when handled or poked, jumping worms “thrash violently, and may jump into the air or even shed their tails,” the website states. The creatures also tend to occur in large numbers, so where there’s one, there are likely more. Soil offers a clue to their presence as well as it becomes grainy, containing castings that look like coarsely ground coffee.

Why be concerned about these worms? For one thing, said Görres, they are detrimental to local ecosystems. “The jumping worms do damage in the woodlands by consuming the leaf litter layer on top of the soil, and then part of the organic horizon, the organic layer in the woodland,” he explained. 

The worms’ activity sets off a series of events that destroys the crucial top layer of soil that contains plant roots, next year’s seed bank, and provides space for new plants to grow. Its destruction allows far fewer small plants to develop, and browsing deer turn to woodier plants for food, letting fewer young maples and other trees grow. 

The worms also appear to damage some garden plants, said Jeanne Atchinson, who manages the Duxbury Community Garden. The worms, she said, are present in the garden that stretches between the Winooski River and River Road. 

They appear to like parsley, she said of the worms. “Parsley would look absolutely gorgeous and I'd start harvesting, and the next thing I knew, I'd come down to the garden and it would be wilted and I’d pull it out and there would be no roots. Like a whole family came to eat that night or something,” she said.  Atchinson noted that she had not seen damage to other plants in the garden.

In Waterbury, no alarms have been raised about jumping worms in the community garden there which is located on the opposite side of the Winooski River not far from the Duxbury garden. But the local A River Runs Through It garden club did not hold its annual plant swap this spring due to concerns about spreading the invasive worms. 

Invasive hammerhead worms are also here, Görres said. These worms are quite different from jumping worms. Hammerhead worms from New Zealand are planarians, or flatworms. Görres described them as true to their name: flat, with hammer-shaped heads. 

Hammerhead worms do not feed on plants, Görres noted. They're predators, consuming other worms and soft-bodied mollusks like snails and slugs. The worms also have the same neurotoxin as pufferfish, but, said Görres, “People will not eat that worm for sure, so it's not a problem, but maybe it gets on other things.”

Görres believes the worms reached North America via trade in horticultural products, appearing in California in the 19th century and elsewhere in the United States by the 1920s and 1930s. Then, Görres said, they spread. 

The worms can make their way into a new garden via “anything where you exchange plants,” and “of course products that are sold can also spread them.”

So far this summer, Evergreen Gardens in Waterbury Center has not yet dealt with the worms, said owner and manager Julia Gill recently. “We haven’t seen any – knock on wood – on our site,” she said. She attributed the worms’ absence to “a fair amount of luck” and frequent product turnover preventing the worms from getting a foothold at the nursery site, but added that their arrival is likely inevitable. 

“We haven’t seen any kind of infestation or anything, but it’s all kind of in the surrounding area, we’re hearing more and more,” Gill said.

For those lucky enough not to have found invasive worms yet, Görres has suggestions to try to keep them out. First, only bring home plants with bare roots. If a gardener purchases a potted plant with soil, said Görres, they should wash off the soil in a bucket of water, then add soap to the water to kill worms. Since soap will not kill the worms’ cocoons (eggs, more or less), the next step is to solarize the removed soil by placing it in a large plastic bag in the sun. Once hotter than 104 degrees, the cocoons will also die. 

Görres recommends a similar process for compost brought in for the garden: Place translucent painters’ drop cloth beneath and above the compost, which should be about six inches deep. Tuck in the sides, Görres said, so worms within can’t escape. This setup should be solarized to kill any worms and cocoons inside for two full days. 

Of course, if the worms are already present, the challenge becomes far greater. Atchinson described one entire gardening season at the Duxbury garden spent trying to drown every worm. “But every worm we came across was a jumping worm, and we couldn’t get any work done, so we sort of decided we kind of had to let it go,” she said. Atchinson said she researched approaches to dealing with the worms, but found nothing conclusive.

Spending hours drowning worms was a dispiriting way to garden. This year, Atchinson said, she is trying a different approach: feeding the worms. A lot. She and other gardeners are using mulch, hay and other materials to enrich the soil and provide plentiful food.

“So I’m kind of hoping that [by] giving them enough to eat and also giving other earthworms something to eat, that this might be okay… we also use manure, we're bringing in a lot of other microbiotic stuff and little critters, little insects, and we're kind of hoping that they'll sort of offset the damage done by the jumping worms as well,” she said.

Atchinson explained the soil at the garden is still recovering from Tropical Storm Irene so it’s important to “feed the soil, get that soil healthy and rich and full of wonderful stuff, and then maybe we'll be able to eliminate a number of issues.” 

Görres shared that a graduate student working with him is currently researching a solution involving growing fungus on millet that kills 80% of the worms. It so far has worked in a greenhouse with specific conditions. The next challenge is figuring out a system that can be easily used by home growers and plant nurseries.

According to Vermont Invasives, the best time to look for these worms is June to September. Jumping worms in particular reach maturity by August and should be easy to spot in late summer and early fall. 

Görres said gardeners shouldn’t despair because the worms have become so widespread. His advice? “When you get them, don't let anybody worm-shame you.”

More information about invasive worms is online at vtinvasives.org.