Amynthas worms have a characteristic white band and are extra squirmy.

Council Member John T. wrote to me after last summer’s ReLeaf Conference. He was surprised that in the conversations he had with other ReLeaf folks, there was little to no awareness of the Amynthas worm (Amynthas agrestis) and how damaging it is to forests, including, one could assume, the urban forest.

Last summer, for the first time, I noticed that my compost-enriched vegetable garden soil seemed excessively granulated, and the soil was subsiding and drying out faster than usual. Turns out, the granulation was the worm castings of the voracious eater, Amynthas agrestis. I’ve since seen the big worms, and now I shudder when they appear. Read on to see why it’s now my mission to rid my garden of these worms, and why the Amynthas worm is a concern for foresters throughout much of the country.

I searched for information specific to the worm’s effects on the urban forest specifically, including by asking our Board members and other colleagues in our field. On Nina Bassuk’s recommendation, I queried Janice Thies, Cornell Associate Professor of Soil Biology in Soil and Crop Sciences and International Professor of Soil Ecology. Dr. Thies says the body of literature about Amynthas agrestis is small and not specific to the urban environment. This major menace just isn’t on the urban forestry radar. I can understand John T’s surprise.

The main ways that urban foresters might accidentally introduce Amynthas worms to the urban forest is via infested plant material and wood mulch. If you have experiences and observations with Amynthas agrestis that shed light on the threat it may pose to the urban forest and its natural areas, please be in touch: [email protected].

Paul Hetzler, Cornell Cooperative Extension (CCE) Natural Resource and Horticulture Educator for St. Lawrence County, wrote the following [excerpted] piece about these troublesome worms. You can also see a new (2017) CCE fact sheet about Amynthas  worms here.

Worms Gone Crazy

The new pest is Amynthas agrestis, a super-size (8-inch-long) earthworm known as the Asian jumping worm, Alabama (or Georgia) jumper, snake worm, or crazy worm. It’s sold as bait, and unfortunately is also hawked as a substitute for the harmless red wiggler used in worm compost bins. Its name comes from the fact that it moves rapidly on top of the soil, resembling a snake more than a worm. Lively and strong, it can flip out of your hand. Other than its impressive squirm factor (in every sense), what’s the problem with Amynthas agrestis—worms are good for the soil, aren’t they?

Not so, my friend; crazy worms are an exception. Here in the Northeast where glaciers scrubbed our bedrock bare a few years back we have no native earthworms. There’s debate, especially in the forestry world, over just how much of a mixed blessing our common, nonnative earthworm species are, but I won’t get into that. Let’s just assume earthworms are good. A native of Japan and Korea, Amynthas agrestis is a very different animal. Its reproduction, for example. Other earthworms are hermaphroditic—that is, they possess both male and female organs, but they still need to breed with another of the same kind. Crazy worms, however, are parthenogenic, meaning they’re all females who spew out cocoons teeming with baby female worms by the hundreds without needing to mate. Ever. All it takes is one to make an infestation.

They also mature twice as fast as European earthworms, completing two generations per season instead of just one. And their population density gets higher than other worms. And remember they’re big. That adds up to an unprecedented worm biomass that will essentially consume all organic matter. This includes your lawn and the roots of annuals, perennials, and shrubs. In the woods, crazy worms destroy native wildflowers, wiping out trillium, bloodroot, Jack-in-the-pulpit, ladyslipper, and other understory plants. Ground-nesting songbirds like the oven bird disappear.

When an Amynthas agrestis infestation removes organics from soil, the soil becomes clumpy and granular and prone to compaction and erosion. Forest soils actually subside, exposing tree roots. Wisconsin Department of Natural Resources invasive species specialist Bernie Williams stated “Their introduction into our state poses a huge threat to the future of our forests.”

Amynthas agrestis can be distinguished from other worms by their darker color (in general), and by the band near their middle called a clitellum. In most worms it’s puffy, and similar in color. In crazy worms it’s even with the body, and milky white to gray. Mature size and behavior also set them apart. Crazy worms are transplants, and that’s how they often spread. Whether in a potted plant from a garden center or a gift from a South Carolina relative, these monsters hitchhike long distances with transplants. They also move from infested areas, mostly in southern states, in shipments of mulch.

There are two ways of telling if your potted plant harbors dangerous fugitives. One is to turn it upside-down and gently remove the root ball. If crazy worms are present, the roots, as well as some potting soil, may be missing. The thing is, there may only be young crazy worms present, or very few, so damage might not be evident. A better solution is a mustard solution. Mix a gallon of water with one-third cup of ground yellow mustard seed, and pour this slowly into the soil. It won’t hurt the plant, but worms (even “good” ones) will come to the surface and you can check for miscreants.

Because of their acrobatics, crazy worms are valued as fishing bait. This is illegal in most places, but it does happen. To be safe, anglers should securely cover bait containers, and destroy all unused bait by placing it on bare concrete and stepping on it. With a presence in Wisconsin and Minnesota, Amynthas agrestis is hardy to USDA Zone 4 and possibly colder.

Here’s an article that summarizes the popular literature available and advises on control (to the extent that is possible) of the Asian jumping worm. The title is “Invasive Worms in Connecticut,” but the information is applicable to New York as well. See also the new (2017) CCE factsheet on this subject.