Invasive Jumping Worms Abound in the Willamette Valley

Some paths at Bowman’s Hill are mostly earthworm castings. Amynthas agrestis, an Asian earthworm, can wreak ecological havoc in North American forests by consuming the litter layer.

An invasive species known as jumping worms, which first arrived in the U.S. in the 1920s as fishing bait and as commuters on imported plants and soils, have been popping up in gardens and nurseries up and down the Willamette Valley, to the potential detriment of plants and trees.   

Jumping worms do more than live up to their moniker — in addition to jumping, they are notorious for their frenzied trashing, slithering, and insatiable appetites. Unlike beneficial earthworms and nightcrawlers that burrow deep tunnels in the soil and release nutrients in the process, jumping worms stay in the debris on top and, with their distinctly large, excavator-like mouths, consume two to three times the amount of leaf litter as other worms, altering native ecosystems as they go. Their tendency to consume so much litter removes mulch that helps cool and conserve moisture for soil, and allows invasive plants and animals to move in. 

The worms’ ravenous feeding isn’t the only thing that has a negative impact on the soil; there’s also their castings, or fecal matter, to worry about. Most worm castings improve soil structure by diversifying the size of soil particles, which enhances moisture penetration and the retention of water. They also contain important microbes that help repel insects and fight soil-borne plant diseases.   

The castings of jumping worms, on the other hand, don’t produce the same beneficial results, due to slight differences in their gut biome. According to Sam Chan, a Sea Grant Extension watershed health and aquatic invasive species specialist at OSU, the castings don’t absorb moisture well, which causes soil to lose porosity and affects its overall structure and composition. These changes can attract certain unwanted microbes, leading to an increased susceptibility to disease and risk of girdling roots, which can restrict the movement of water and nutrients to leaves. 

With the loss of leaf litter and changes to soil structure that jumping worms can cause, plant stems and roots at the surface of the soil may become more exposed to environmental extremes. Though it’s difficult to ascertain the exact number of jumping worms currently in Oregon, the first reported species, an Amynthas gracilis, was found in 2016 in Grants Pass, where it was passed along through compost. Another species, Amynthas agrestis, has since been detected in at least six counties along major transportation routes, likely having arrived as tiny cocoons in plants, soil, mulch, and tire treads from the East Coast. These cocoons typically hatch in spring; larvae begin feeding, grow rapidly into adults, and die in the winter after laying more cocoons — and so the cycle continues. 

According to Chan, while it’s likely that the jumping worms are here to stay, people can still pick up habits that help minimize their spread, such as by shaking off the roots of plants when sharing or buying at a private plant sale and buying barefoot plants when possible. Chan also recommends refraining from sharing compost, mulch, soil, or plants that contain a known infestation. Those who find jumping worms in their garden can brush off their shoes and equipment when moving from place to place to prevent them from spreading.   

If anyone finds jumping worms, they can report it to the Oregon Invasive Species Council’s hotline 866-INVADER (268-9219) or online. An informative guide, developed in partnership with Chan, is available to help people identify jumping worms in the Pacific Northwest. In addition, for more information on how to avoid spreading invasive species in plant sales or swaps, readers can check out this article.  

By Emilie Ratcliff