By Tim King
Non-native earthworms, Amynthas agrestis, were greeted with some hysterical, and inaccurate, media reports when they were first observed in appreciable numbers at the Viles Arboretum in Augusta, Maine, and several other locations in Augusta and in Portland a decade ago. Seemingly reputable news sources claimed that Amynthas worms, commonly called jumping worms, could jump as much as a foot. One headline writer described them as “earthworms on steroids.” Amynthas worms do not use performance-enhancing drugs, but they do have the capacity to drop their tails when threatened as a defense mechanism.
The truth is that all of Maine’s earthworms aren’t really Maine’s worms. Maine doesn’t have a native earthworm species thanks to the glaciers that ground their way through the state over 10 millennia ago. Species native to the southeastern United States have been creeping their way north as the centuries pass by but, at last check, none had made it further than Pennsylvania. Any earthworm north of the Pennsylvania-New York line has been carried there by humans, and the common earthworms (Lumbricus terrestris, or nightcrawlers) are thought to have been transported from Europe by way of colonial trading.
The Amynthas worms now found in Maine are native to Korea and Japan and were carried here in the soil of pots containing non-native plants imported from those areas. The oldest Amynthas record, predating those early Augusta and Portland populations, is from a coastal Maine greenhouse in 1899. Although there is another record of Amynthas from a greenhouse, in 1952, the worms stayed pretty much out of sight for over a century.
However, greenhouses, and non-native plants, continued to be a significant vector of spread as Amynthas came out of obscurity and populations increased rapidly in the last 15 years.
“The spread appears to be closely associated with horticulture,” Gary Fish, the State Horticulturist in the Department of Agriculture, Conservation and Forestry, and Brittany Schappach, of the Maine Forest Service, wrote in a co-authored report, entitled “2024 Jumping Worm Update,” earlier this year.
Fish and Schappach report that home gardens and compost piles were by far the most commonly observed environments with Amynthas worm sightings during a 2022-2023 survey. Lawns, however, also had a significant number of recorded sightings.
“Some lawns have a thick thatch layer and the worms would be happy to eat all those dead grass crowns,” Fish wrote in a series of email interviews. “They have been found in turf, but I don’t think it is an ideal habitat for them, they’d probably prefer compost, mulch, or leaves.”
Amynthas worms eat plant detritus and, generally, live in the top 1 to 3 inches of leaf litter, lawn thatch, or garden debris. That zone, when speaking of forest soils, is referred to as the “epigeic soil zone.”
Given adequate detritus and environmental conditions Amynthas worms, which are parthenogenetic, meaning they can reproduce on their own without a mate for fertilization, can possibly produce two generations per season. According to Fish and Schappach, they live as tiny egg cocoons during the winter and hatch as juveniles during May and June. They become adults capable of asexual reproduction in September and only live long enough to reproduce themselves.
“Cocoons are the real problems,” Fish and Schappach wrote. “Some are as small as a couple of millimeters. They are difficult to see, easy to spread, and resistant to cold.”
The worms also have the capacity to build up a cocoon bank, similar to the seed banking of many weed species, they added.
This life cycle makes for an organism that is easily spread by human activity and extremely difficult to control. Fish and Schappach, in their 2024 report, wrote that Amynthas worms have spread from just a few locations in Augusta and Portland in 2014 to recorded sightings in all but one or two Maine counties in 2023. Not only are the worms increasingly widespread, the two described the overall number of 2023 sightings as a “surge.” For example, the 309 reported sightings in 2023 accounted for nearly a 700% percent increase over 2021’s 39 recorded sightings.
Most worms are being spotted in Maine’s more highly populated counties. Cumberland, Maine’s most populous county, has the most recorded sightings, with a total of 101. The southernmost county of the state, York, has the second highest numbers of humans and its 66 recorded sightings suggest it has the second largest Amynthas population. Somerset County has far fewer people and, if its two recorded sightings are an indication of its worm population, far fewer jumping worms.
“We don’t have enough data to be sure of how widespread the worms are in the more northern and rural counties,” Gary Fish said. “Since the worms are spread by people it only follows that we would find more in the counties with higher populations or those with more landscape and gardening activity.”
As researchers and regulators work to learn about the scope of Maine’s growing Amynthas population, Fish points out that no known controls have been approved by federal or state regulators.
“People are trying things they hear about on social media, but they really should not be using those methods until they have been researched and approved through risk assessments done by EPA for pesticide registration,” he said.
For example, Fish has seen tea seed meal extract suggested as a control for jumping worms by a number of people. He doesn’t recommend using it. “It has never been researched to see what non-target organisms are affected,” he said. “I don’t recommend even using soaps, salt, or diatomaceous earth either. Those are all broad-spectrum controls that will kill many other organisms that may be beneficial.”
Even though the Amynthas worm population in Maine has increased rapidly it is not regulated and has not been officially designated as an invasive species in the state. Fish, Schappach, and their colleagues are largely limited to educational, monitoring, and research efforts. Under the current circumstances Fish does not believe an invasive species designation would be feasible.
“The regulation of invasive species is hampered by the lack of human and financial resources,” he said. “We would not have the resources to enforce a quarantine or other measures to slow their spread.”
Fish points to the actual, and potential, significant environmental and economic costs of non-native species, such as Amynthas worms, and recommends a governor’s level invasive species advisory council to help facilitate multi-agency responses. In a 2022 paper, entitled “Should Maine Develop a More Comprehensive Approach to Invasive Species Management?,” he points out how the state of New York took such a comprehensive approach to invasive species management.
Jumping worm cocoons can be spread by humans in soil materials such as compost and potting soil, fishing bait, potted plants, on logging and farming equipment, and even on hiking boots. To effectively control them in Maine, and their environmental and economic damages, according to Fish’s recommendations, multiple state agencies would have to collaborate and work across jurisdictions.
The environmental and economic damage that Amynthas worms could cause in Maine’s forests is significant. Although there were only 31 recorded sightings of the worms in Maine’s woods in 2022-2023 that is more than enough to establish a destructive population.
Amynthas worms in deciduous forests can cause reduced understory diversity, reduced insect diversity, and an overall reduction in biological diversity, from ground-nesting birds to salamanders, according to Fish and Schappach’s 2024 report. The depletion of leaf litter can expose tree roots and lead to soil compaction and erosion.
“It appears that the castings of these earthworms are very erodible. Erosion diminishes the quality of soils in forest and also takes sediments into water bodies where the sediments and the nutrients contained in them are pollutants,” said Josef Görres, who, along with postdoctoral researcher Maryam Nouri Aiin and doctorate student Madelynn Edwards, is researching, at the University of Vermont, how Amynthas worms spread, how to control them, and what their impact is on natural resources such as water and soil quality.
The potential for degraded forest soil quality from Amynthas worms poses a threat to the ecological health of sugar maples in the northeastern states, according to Görres’s research.
“The main risk that they pose to sugar bush is that maple regeneration is lower when they are present,” he said. “The worms change the forest floor structure by producing these loose castings and they consume the upper organic horizon. This is where seeds are stored and where seeds of typical deer browse species germinated. With those species gone deer will start feeding more heavily on woody saplings just because that is what is left.”
The degradation of forest soils by Amynthas worms can set the stage for erosion as well as the further spread of the worms. “Another major way to spread them is by the movement of water and erosion,” Görres said. “In big storms, soils can be eroded and the jumping-worm-invaded soils are particularly susceptible. The sediments often contain worms and their cocoons, and they end up in flowing water such as streams, which then take them to areas further downstream.”
Like Gary Fish, Görres points out that there are no approved controls for Amynthas. However, the Görres Lab at the University of Vermont is looking at a number of approaches to controlling the worms, including Integrated Pest Management and a fungus, Beauveria bassiana, that may work as a biopesticide.
“It is registered as an insecticide, but it seems effective on jumping worms, too. Because it is not registered for worms it is currently still illegal to use as vermicide,” Görres said. “We also look at controls like heat, using solarization, or tillage as ways to keep their numbers down.”
While research for Amynthas controls by scientists is ongoing, both Fish and Görres recommend that everybody take common-sense measures to slow the spread of the worms.
“I just talked to a colleague in New York who has seen them introduced to a forest at a fishing site near where her research plots are,” Görres said. “Don’t use them for bait. They are not good angling worms anyway.”
While not many worm sightings have been recorded in agricultural settings, farms that generally have more plant debris associated with their practices can be at risk of establishing populations. Görres said he’s aware of some sightings in “sustainable agriculture” settings, and Fish said there have been recorded sightings of the non-native earthworm in commercial vegetable operations in Maine. If farmers make their own compost, Fish recommends keeping it onsite.
“You may already have them and just have not seen them,” Fish said. “Keeping everything onsite is very helpful. It is very easy to import them to another location.”
In their report, Fish and Schappach recommend trying to follow a simple mantra to avoid importing or exporting the worms: “Arrive clean, leave clean.” To arrive clean, they recommend checking your footwear, vehicle, tools, and equipment to be sure they are free of soil or compost residue. To leave clean, check those things and also determine if any nursery stock or potted plants are free of worms and cocoons. Since cocoons can be nearly impossible to spot, they recommend buying bareroot stock, if possible, or only buying potted plants or seedlings in pasteurized or sterilized soil. Even ground hardwood mulch can be a vector for spreading Amynthas, they warn. Cocoons can be destroyed by heating the mulch, or potting soil, to 104 degrees Fahrenheit for four days, according to Fish.
If you do end up with Amynthas worms in your yard or garden, or on your farm, the first sign may be the presence of worm castings, which have a distinctive granular appearance like used coffee grounds or ground meat.
For a closer examination you can follow this test from the University of Maryland Extension Service:
“Mix ⅓ cup of ground hot yellow mustard seed (look for Chinese or Asian hot mustard) into 1 gallon of water and pour half of the liquid slowly over a 1 square foot of soil you want to test. Wait a few minutes and pour the rest. This will make worms (any earthworms) come to the surface. Identify, collect, and discard jumping worms, if present. The mustard solution will not harm plants or kill the worms.”
More than one species may come to the surface. If there are Amynthas worms, on a warm day, they will be highly active and make thrashing serpentine movements. If you do your mustard test in the fall, the jumping worms will be mature with a white or gray clitellum, a collar-like band, on segments 14 through 16 that fully encircles the worm.
If you do discover that you have jumping worms on your property, Fish asks that you fill out the Maine Jumping Worm Report Form found at maine.gov/dacf/php/gotpests/othercritters/worms.
About the author: Tim King is a produce and sheep farmer, a journalist, and cofounder of a bilingual community newspaper. He lives near Long Prairie, Minnesota.
This article was originally published in the fall 2024 issue of The Maine Organic Farmer & Gardener. Browse the archives for free content on organic agriculture and sustainable living practices. Subscribe to the publication by becoming a member!
