Invasive ‘Jumping’ Worms Are Now Tearing Through Midwestern Forests

The voracious crawlers are now chewing through leaf litter in Minnesota and Chicago and disrupting understory where some birds nest.

The writhing worm in ecologist Brad Herrick’s hand is stillfairly newin town, but it’s taken only a few years for its kind tocollectively damage swathsof the University of Wisconsin–Madison Arboretumwhere he works. Theunassuming invertebratesfirst arrived to thisforest—a of sugar maple, beech, yellow birch, and hemlock intended tomimic the state’s hardwood forests—in 2013, concealed inan order of mulch that carried castings of the invasive worm. Arboretum naturalists knew they were dealing with Asian jumping worms, but they had no idea how to stop them from taking over.

Until recently, these forests' soils were largely wormless. During the last ice age, which ended roughly 12,000 years ago, glaciers wiped out earthworms in what is now the northern United States. Absent the wriggling decomposers, forests evolved to rely on to break down leaves and twigs that litter the floor. Earthworms found in U.S. soils today are mostly invaders from Europe, but in the last fewdecadesmore than a dozen species of jumping worms—a more destructive group from Asia used as bait or in commercial mulch—have spread. In the 1990s, scientists began documenting their damage to forests in , the , and . Now,theworms have made it to the Upper Midwest, and scientists fear theinvaders will inextricably alter the region'sforest floor ecosystem and harm birds that nest there.

Oncelet loose, jumping worminvasions are hard to contain. Where most European worm species move about 30 feet per year, jumping worms , or roughly the size of 13 football fields, of new ground in a single season. In Illinois, experts confirmed the presence of jumping worms, also known as Alabama jumpers, crazy worms, and snake worms, in 2015. In the past year, first reports of the worms have come out of counties in Minnesota, Iowa, and Wisconsin, and this August scientists in Chicago that jumping worms had effectively invaded the entire city.

According to Scott Loss, a conservation biologist at Oklahoma State University, the spread of jumping worms could exacerbate the impact other invasive earthworms have already had on forests in eastern and Midwest forests.

“It's like stepping on the gas pedal to decomposition,”Loss says. “Earthworms simplify what would otherwise be distinct [soil] layers. They mix that up and turn an otherwise diverse soil structure into a homogeneous mass.”Jumping worms have a particular talent for leaf processing. Unlike their European counterparts which burrow deep beneaththe forest floor, jumping worms stay on the surface, rapidly consuming leaf litter and turning the once cohesive mass of soil into tiny crumbles that easily erode. One study found that jumping wormscan eliminateup toof leaf litter in the forests they invade. As a result, organic matter in this layer doesn't have a chance to decompose and returnits nutrients to the terrain. In this altered soil it’s difficult for the goblin ferns and asters that line healthy forest floors to take root, Loss says.

Such losses may have ripple effects on ground-nesting birds, which rely on these plants to conceal their eggs from predators. Scientists haven't studied the avian impacts from jumping worms yet, butresearchon European earthworm invasions provides a hint.In a 2012Loss found that populations of Hermit Thrushes and Ovenbirds were significantly lower in forested areas of Minnesota and Wisconsin where these earthworms were present.Loss predicts that earthworms could eventually cut the population of Ovenbirds byin maple and birch forests.

Due to their ultra-destructive tendencies, it’s likely that jumping worms will permanently uncover more nesting territory and make things even worse, he says. Other songbirds such as Black-and-white Warblers and Canada Warblers, as well as game birds like Ruffed Grouse, could also experience suchconsequences.

The bugs that feed some forest-dwelling birds could also take a hit. In Appalachia, Asian jumping worms have already signficantly reduced populations ofandin some areas.Loss notes that earthworm-eating birds like the American Woodcock, which foragefor earthworms buried beneath thickets, could benefit from the new food source as long as they can adapt to the invasive cuisine. They may be forced to: Once they invade an area, jumping wormsother worms.

Whether or not jumping worms could make a nice meal for some birds, stopping the invasive species from spreading is imperative, says Lee Frelich, director of the University of Minnesota Center for Forest Ecology. His team hasfound some evidence that hotter and drier soils limit theworms' success, which could slow their spread in his state. If histeam can determine just how hot, cold, or dry soil needs to be to keep Asian jumping worms out, they’ll be able to predict where on the continent the worms are most likely to spread to focusmonitoring and eradication efforts.

In the meantime, researchers at the University of Wisconsin and the University of Minnesota are experimenting with using pesticides made with saponin, a chemical compound found in tea and maple leaves. Saponin-based pesticides are favored by golf course keepers trying to keep worms off the green, as opposed to more toxic chemicals often used in backyards. “Because it naturally occurs in plants, we hope saponin can control the worms without disrupting the ecosystem,” Frelich says. “There are a lot of poisons we could use, but they’d kill everything else, too.”