Jumping worms, a damaging invasive species that first arrived in the United States in the 1920s as fishing bait and as hitchhikers on imported plants and soils, have established themselves in gardens, nurseries and forest edges across Oregon.

Jumping worms are part of a growing problem across North America. As members of the genera Amynthas and Metaphire, they are known to displace European earthworms, degrade forest floor structure, alter nutrient cycling and reduce biodiversity. In Oregon, their spread has implications not only for gardens and nurseries but also for native plants, wildlife habitats and overall soil health.

Unlike beneficial earthworms and nightcrawlers that burrow deep tunnels in the soil -- helping aerate and release nutrients -- jumping worms remain in the debris layer on the surface and consume two to three times more leaf litter, according to Sam Chan, Oregon State University Sea Grant Extension watersheds and aquatic invasive species specialist.

Native to parts of Asia, jumping worms are easily identified by their vigorous thrashing, slithering and even leaping behavior. They are smooth, glossy gray or brown and range from 1.5 to 8 inches long. A clear identification feature is the clitellum (band), which is milky white to gray, smooth, and completely encircles the worm's body. In contrast, the clitellum of common earthworms is raised and does not wrap fully around the body.

Jumping worms possess large mouths, like mechanical excavators, allowing them to consume significant amounts of material. Their feeding behavior outcompetes native microbial organisms and invertebrates that other species rely on. Their appetite also strips leaf litter, leaving bare soil that encourages invasive plants and animals, disrupting native ecosystems. They remove mulch that helps cool soil and retain moisture.

In addition, worm castings -- the fecal material of most earthworms -- typically contain beneficial microbes that fight soilborne diseases and deter insects. Castings also improve soil structure by diversifying particle size, enhancing moisture penetration and water retention. Jumping worms, however, have a different gut biome that leads to opposite outcomes.

"What they are casting out doesn't absorb moisture well, so you end up losing porosity, which affects the overall structure of the soil," Chan said. "Initially wet and gummy, the castings quickly dry into hard granules that are difficult to rewet -- not the best medium for growing plants."

Soil structure and composition changes caused by jumping worm castings can attract unwanted microbes, increasing disease susceptibility and leading to girdled roots. Plant stems and roots may become exposed to environmental extremes due to the loss of organic matter and protective mulch.

The first confirmed jumping worm in Oregon -- Amynthas gracilis -- was found in 2016 in Grants Pass, passed along in compost. Another species, Amynthas agrestis, has since been detected in at least six counties, from Pendleton in Eastern Oregon to Roseburg in Southern Oregon, primarily along major transportation corridors.

Although cold winters typically limit their spread, milder conditions in the Willamette Valley might allow jumping worms to survive in sheltered areas, making them more persistent than previously assumed.

Because they are hermaphroditic, jumping worms reproduce easily. They lay tiny cocoons with two or three embryos inside, which hatch in spring. The worms feed and grow rapidly into adults, die in winter and leave behind cocoons for the next generation.

Jumping worms have been outlawed in many states but are still legal in some and can still be purchased online for fishing. Chan advises against buying jumping worms -- also known as crazy worm, Asian jumping worm and snake worm -- and encourages raising awareness about their impact. Many people, including some sellers, are unaware of their invasiveness.

"Jumping worms are probably here to stay," said Chan, an assistant professor in the Department of Fisheries, Wildlife, and Conservation Sciences in the College of Agricultural Sciences. "We want to minimize their spread. You won't want them to get established in your garden. I sure don't want them in my garden. Escaped worms, releasing leftover bait worms and unknowingly spreading them through plant materials and soils can have serious negative impacts to native and planted landscapes."

To help reduce the spread of jumping worms:

If you find jumping worms, report them to the Oregon Invasive Species Council hotline at 866-INVADER (866-468-2337) or online.