Good Year for Jumping Worms, Bad Year for Forests

By Cynthia Drummond for BRVCA
August 24th 2024

RICHMOND – Invasive jumping worms are making themselves at home in the Eastern United States, destroying not only garden soil but the forest floor.

Known to scientists as Amynthas agrestis, jumping worms writhe and squirm, giving them their common name. They are native to Asia, and have been in North America since the early 1900s, when they arrived in the soil of imported potted plants.

Like other earthworms, the castings of jumping worms are nutrient-rich, but they have a coarse texture that alters the structure of the soil, rendering it unable to hold nutrients. The worms also consume great quantities of leaf litter, or duff, on the forest floor, exposing tree roots, and increasing erosion, which alters entire forest ecosystems.

Soil scientist Josef Görres, formerly of the University of Rhode Island and currently at the University of Vermont, studies jumping worms and their impacts on forests, agriculture and gardens.

Görres assesses jumping worm populations each month, and advises growers and owners of composting and mulch operations on how to identify and control the worms and their cocoons. The worms are of particular concern to maple syrup producers, because they impact the forests where the sugar maples grow.

This summer’s excessive rain in some areas, including Rhode Island, has helped disperse the invasive worms.

“Moisture can also move them,” Görres said. “So, you have lots of rainfall on a slope and they move down the slope. …They wash down, and sometimes they get into a river and the river takes them to other places. They can survive in water for a long time, so the river might actually take them to another place where they haven’t been before.”

Identification

In addition to their unusual behavior, jumping worms can be identified by the colored band, or “clitellum,” near the head, which completely encircles the worm’s body. In earthworms, the clitellum goes only part way around the body, resembling a saddle, rather than a band.

Jumping worms reproduce asexually. The worms die in winter, but their microscopic cocoons remain in the soil, hatching in May.

“You start off with very few worms,” Görres said. “In May, you have 50, 60 per square meter, then you have 150-200 per square meter in the middle of June, and then, at some point, those numbers go down again to something like 100, in July. Then in August, you get the first adults, so they start reproducing, and then in September, you have all adults, and they produce really fast. They produce a lot of cocoons in September, October, and then the number of cocoons produced goes down in November.”

How Do We Kill Them?

Researchers have found that exposing the worms to temperatures of 104 degrees Fahrenheit or greater will kill them.

“That is currently the magic number,” Görres said. “We’re finding out whether or not they can be killed at something like 95 degrees Fahrenheit and, I think that’s possible. There was a study in 2009 that said the worms will die at 95. There’s no survivors at 95 degrees.”

Rhode Island’s sweltering summer, then, might have been helpful for short - term jumping worm control - if it hadn’t been for all that rain.

“If you had a drought, as well as hot weather, then maybe you wouldn’t see many of them this year,” Görres said. “But, the following year, you’d see a lot again, because the cocoons last for longer than a year and they have ways of surviving droughts and cold weather. So, it’s complicated.”

The Rhode Island Wild Plant Society canceled its Aug. 23 plant sale after jumping worms were found in some of the plant trays.

Görres explained that the worms can easily enter plant trays or pots, even if they are on pallets, so it is always safer to keep plants higher, on potting benches or tables.

Gardeners should wash the roots of newly-acquired plants sold in pots. Even safer, Görres added, is to grown plants from seeds or cuttings.

“Cuttings that have been rooted, so bare root stock,” he said. “I think that horticulture is responsible for a lot of the spread, for sure. And, the sad ting is that there’s little they can do about it right now. I would say that customers of nurseries should learn to check for worms in the pots and maybe learn how to best root - wash the soil. You buy the plant, you take it home, you root - wash it. You put whatever debris you get out of the pots, the soil that’s around the roots, store it somewhere in water and put a lid on it so any kind of worm that comes out of it doesn’t get out.”

When the washing water has evaporated, the material left behind should be solarized, which involves subjecting it to heat from the sun. The same method is recommended for compost.

The first step is to spread a thin layer of compost, no more than eight inches, in a sunny area, on a flat surface like cardboard, which will insulate the compost from the cooler soil underneath.

Enclose the compost with plastic. The compost must heat to a minimum of 104 degrees to kill the worms and cocoons. This can take a few days, depending on the weather and the time of year.

More information on solarization and other control measures is available on the University of Maryland Extension website.

What About Chemical Controls?

There are no chemical controls approved by the Environmental Protection Agency for jumping worms.

Görres has joined researchers from Nova Scotia to Minnesota in forming the Healthy Soil Collaborative to try to find solutions to the jumping worm problem.

“My group is working with people in Minnesota, and we’re testing a bunch of pesticides that are minimal risk, by EPA standards,” he said. “… The regulators and industry are always a few steps behind the invasion, right? So, it takes time intervene in an invasion when the first worms, or the first pests, appear. …We are not equipped to mitigate the problem, because there’s regulations in place that get in the way. The regulations are there for good reason. There’s human health concerns, there’s concern for other organisms that might be affected by the organism that you’re trying to apply to the worms. So, there’s good reasons why these regulations are there, but there’s also good reasons for using some of the pesticides when the problems just starts. Now, it’s very difficult.“

Home gardeners can help control the worms, but it is a challenge to persuade people to go to the trouble of examining new plants, mulch, soil and compost and washing the roots of new plants they buy.

“That is a problem,” Görres conceded. “People will say ‘what do I care about jumping worms?’ especially in a state that is urbanizing, where maybe, the forest is not valued so much, you know.”