Pictured Above: CHANGING THE SOIL. Jumping worms change the soil structure, according to Tricia Bethke. In an analysis of infested soils, she found that the percentage of small soil aggregates (less than 0.5 mm) decreased and large aggregates (2-4 mm) increased. The long-term impact is not known.
Earthworms have earned the affection of no-tillers because they turn crop residues into plant nutrients and deftly mine channels in the soil to clear the way for air, water and root systems.
But some ecologists are sounding the alarm about so-called jumping worms — also known as ‘crazy’ worms, Alabama jumpers and snake worms. Jumping worms are an invasive family of worms that have the potential to alter the chemical and physical properties of soil.
The name “jumping worms” may be a bit misleading. They don’t jump per se, but they do thrash violently when disturbed. “The thrashing back and forth, I think, is probably a defense mechanism that keeps birds from eating it,” says Tricia Bethke, forest pest outreach coordinator with The Morton Arboretum in Lisle, Ill. “They thrash a lot at first, but if you hold them in your hand for a while, they become very docile.”
Native to southeast Asia, jumping worms were most likely introduced in the U.S. through contaminated nursery stock, according to Bethke, and they’ve been here for decades. At least 16 species exist in North America, mostly in the genus Amynthas, but the most common ones are Amynthas agrestis, A. tokioensis and Metaphire hilgendorfi, which are frequently found living together, she says.
Currently, these worms are found in at least 17 states, including Oregon, Minnesota, Wisconsin, Illinois, Michigan, Ohio, New York, New Jersey, Vermont, New Hampshire, Connecticut, Massachusetts, Maryland, North Carolina, South Carolina, Georgia and Tennessee.
Not Your Grandpa’s Earthworms
The spread of jumping worms is mostly of concern amongst forest ecologists, as that is the primary ecosystem where they’ve made an impact so far. Few populations have been documented in cropland to date, according to Brad Herrick, ecologist at the arboretum at the University of Wisconsin-Madison.
Jumping worms range in length from about 1½-8 inches. According to Eileen Kladivko, professor of agronomy at Purdue University, they look similar to the European worms that we’re familiar with in the U.S. (there are relatively few native worms in glaciated areas of North America), but they usually have a pale band near the head (called a clitellum) that completely encircles the body and is milky white or gray and smooth (not raised and only partially encircling the body as with the European worms). The lower part of the body, below the clitellum, is usually a brownish gray, as opposed to pink or red.
Unlike night crawlers and some other European worms, jumping worms don’t burrow underground and don’t aerate the soil. Rather, they inhabit the top 1-2 inches of organic matter and topsoil.
In addition, they are asexual, so they don’t need to mate to reproduce, and they have an annual life cycle. “They hatch from cocoons in late spring, mature after a few months and then start laying more cocoons before dying after the first hard frost,” says Herrick.
Increased Soil Nutrients
The reason jumping worms could pose a threat to no-tillers is because they’re voracious eaters of organic matter, and as such, they can cycle through residue on the soil surface very quickly, leaving behind loose, friable piles of nutrient-rich castings.
A 2016 study by Jiangxiao Qiu and Monica Turner, researchers from the University of Wisconsin, explored the effects of jumping worms on forest and prairie soils. Over the course of the 4-month study, they found forest soils invaded by jumping worms had significant increases in soil organic matter, carbon, nitrogen (N) and available phosphorus (P). Though less substantial, invaded prairie soils showed similar increases in everything but P.
This may sound like a boon, but Herrick isn’t so sure. “Because these nutrient-rich casts are loose and distributed in a more or less uniform layer on the soil surface, they’re highly susceptible to erosion,” he explains. “Also, since most of the casts are produced later in the growing season and are not readily incorporated into the soil profile, they are not always available for plant uptake.”
Keep Them at Bay
While jumping worms as of yet are uncommon in cropland, and there’s no guarantee that they won’t become invasive in farm fields in the future, certain indicators suggest farmland may not be the ideal environment for them.
According to Qiu, jumping worms seem to prefer forest soils, which tend to be easier to burrow into, rather than prairie soils that have more dense root systems. In addition, forest soils are moister and cooler than prairie soils.
While more study needs to be done, Herrick suggests that crop residue might not offer the ideal diet for jumping worms. “They need a continuous organic layer,” he says. “A no-till system might provide that, but not all crops will likely have the same palatability. For instance, corn stalks probably wouldn’t be a good food source, unless they were allowed to break down for a year or more. Maybe soybeans would be more palatable, but there is little to no research that has addressed that.”
At the moment, there are no treatments to eradicate jumping worms, so the best plan is to avoid introducing them into the environment, says Bethke, who adds that the main ways they’ve been introduced in recent past has been through cocoons in mulch or compost or from discarded fishing worms. A. agrestis and its relatives are sometimes sold as good vermicomposting worms because they cycle through organic matter very quickly, and presumably, their active thrashing is attractive to fish.