Whether you’re a professional grower or more of a casual backyard gardener like I am, you’re likely already on the lookout for various invasive plants and insects. Many of these are simply nuisances which we eventually learn to manage. But others—including the species collectively known as Asian jumping worms—are doing significant damage to our forests and farmland.
Some researchers suggest that at least three Asian jumping worm species may have arrived along with Japanese cherry trees donated to Washington, D.C., and Bethesda, Maryland, in the early 1900s. In the ensuing decades, many more jumping worms have hitched rides in potted plants and bagged soil products imported from Asia.
Warming temperatures and changing weather patterns also may contribute to the spread of these invasives. At present, various Asian jumping worm species have been discovered in nearly 40 states and in southern Canada.
It’s worth noting that, although we expect to see nightcrawlers and other types of earthworms slowly plowing through the organic matter in our soil, “our” worms aren’t native to North America either. During a December 2022 presentation on Asian jumping worms, Bob Bruner explained, “The worms that we have [in the United States] are almost entirely European worms.”
Bruner serves as exotic forest pest specialist in the Department of Entomology at Purdue University. He continues, “Most of the North American native worm species were eliminated in glaciation.” Although European worms aren’t native to the U.S., Bruner says, “They have adapted to our environment over the course of several hundred years. European worms can help aerate soil—they can do a lot of beneficial things. Whereas Asian jumping worms ruin soil in terms of being able to develop plants that we want there.”
To understand why Asian jumping worms are so problematic, it helps to compare their habits and lifecycle to those of European earthworms.
Differing Habits, Lifecycles
Unlike European worms, Asian jumping worms remain at or very near the soil’s surface—usually in very large numbers. As a result, they can quickly devour many layers of leaf litter. They then leave large quantities of grainy, nutrient-poor castings behind. Soil that is infested with Asian jumping worms may have the consistency of finely ground coffee or sand. It is more susceptible to erosion and the effects of drought.
By contrast, European worms tunnel up and down through the top 4 to 6 feet of soil. After feeding on dead plants and leaves above ground, these earthworms burrow back down, creating vertical channels as they go. These channels benefit plants by facilitating improved aeration as well as access to water and nutrients via the worms’ nutrient-rich castings.
“European worm castings … tend to be partially digested,” Bruner says. “They provide nitrogen in a way that’s more easily accessible by plants.”
For now, adult jumping worms can’t survive the hard freezes of winter. But their egg casings can successfully overwinter even in very cold climates. (Depending on the species, a single jumping worm may be able to produce 10 to 50 cocoons per year.) What’s more, these cocoons are tiny—and, therefore, easily moved from place to place in soil, compost, leaf litter and even via the soles of our shoes.
Spotting Jumping Worms
While European earthworms gradually propel themselves through the soil, jumping worms flip and slither with snake- or eel-like movements. (In fact, they’re sometimes also called “disco worms,” “crazy worms” or “snake worms” because they can move so erratically.)
Aside from their unusual movements, jumping worms also look markedly different. While European earthworms are reddish-pink, segmented and moist, Asian jumping worms range from dark brown to dark gray and look much smoother. The jumping worm also has a very noticeable, light-colored band that wraps all the way around and is flush with the rest of its body.
On a European earthworm, this band is slightly raised and its color doesn’t contrast as much with the rest of its body.
The best ways to prevent the spread of jumping worms? Purchase bare root stock rather than potted plants in order to avoid potentially infested soil. Also, use only your own compost or compost from a trusted source.
If you purchase bagged compost, soils or mulch, leave the bags out in the sun for several days. Extreme heat will kill Asian jumping worms and any cocoons that may be present.
Finally, if you discover that Asian jumping worms have already made their way to your garden, contact officials at your local extension office for guidance.