Earthworms from Europe are changing our boreal forests

Canada and some parts of the United States are facing an invisible threat from below.

No, it's not some tunneling terrorist cell. And building walls won't help.

Researchers at Ohio State University, the University of Alberta and Simon Fraser University in British Columbia have identified invasive earthworms in parts of North America, including Ohio.

The first stages of the research began in 2006, when Erin Cameron, then a doctoral student at the University of Alberta, and her team examined various sites along the boreal forest in northeastern Alberta in Canada and found that earthworms were more common around older roads than newer ones.

Cameron, who is now a post-doctoral researcher at the University of Helsinki, looked specifically at the Dendrobaena octaedra, a member of the European invasive family Lumbricidae.

These earthworms are epigeic, which means they don't burrow below ground. Instead, they tend to stay in the leaf litter on the forest floor and in surface soil, said Peter Ducey, a biological-sciences professor at the State University of New York-Cortland.

The worms - about 1 inch long - eat the leaf litter, destroying the habitat of some nesting animals, including salamanders and birds.

Forest floors are carbon sinks, which means they hold in carbon dioxide. The worms' activity releases carbon dioxide into the atmosphere, which affects warming and climate change.

"When you add them to a system they've never been in before, they can alter the dynamics . . . and make it less hospitable for native species," Ducey said.

According to samples sent from citizen scientists to the Great Lakes Worm Watch project at the University of Minnesota-Duluth, there have been Dendrobaena octaedra sightings in Ohio in the past 10 years.

Ryan Hueffmeier, an education specialist at the Natural Resources Research Institute at Minnesota-Duluth, said the project's main aim is to educate people and locate earthworm species within the Great Lakes region.

At this point, he said, European earthworms such as Dendrobaena octaedra are established in the region, while the more invasive Asian species in the Amynthas family are not - at least not yet.

The research project currently is focusing on locating these species to help curb the spread.

"It's a fairly large problem, one that is not well-studied," Cameron said.

Cameron used her initial findings as a basis for the research model and collaborated with Oksana Chkrebtii, an associate professor of statistics at Ohio State, to create simulation models that show how far the worms would spread in the boreal forest and how long it would take.

One of the main challenges, Chkrebtii said, is determining when exactly a species is introduced given that earthworms mainly spread through the soil.

"Invasions occur over time, and they're not observed most of the time," she said. "Earthworms have been invading North America for a very long time, and it's hard to determine when they were introduced (and) at what rate they were introduced."

Chkrebtii used data from 78 sites to create models to predict the spread of earthworms 50 years from now.

Her model shows the initial arrival at a specific road and projects its spread given different rates of introduction and movement.

Cameron and Chkrebtii compared results from the model with the actual data to check for close patterns. The suggested spread rate the model came up with was about 52 feet per year, with an introduction rate of close to four worms every 60 miles.

These rates were then used to model the future spread of earthworms, specifically in northern Alberta. The model predicted that by 2056, about 39 percent of the nearly 15 million acres of forest habitat likely will have established populations of the earthworms.

Right now, the earthworms are in about 3 percent of the forest.

Chkrebtii said the Great Lakes region is similar to the boreal forest in northern Alberta.

One of the ways earthworms move and end up near roads is via car tires, Cameron said. Worm eggs - about the size of a sesame seed - are picked up in tire-tread grooves and moved from one place to another.

Since earthworms often are used as bait, fishermen also move them from spot to spot, inadvertently helping the species spread.

Peter Groffman, a senior scientist at the Cary Institute of Ecosystem Studies in Millbrook, N.Y., said the first non-native earthworms likely arrived with plants the first European settlers brought with them.

He said the problem primarily exists in areas north of the glacial boundary, which includes the Great Lakes region.

Groffman said the area likely once had native earthworms, but they were killed off when glaciers flowed through the region thousands of years ago. Over the years, the forests' ecosystems developed without the worms.

Rebecca Pinder, an assistant professor of biological science at Columbia-Greene Community College in Hudson, N.Y., said forests in Ohio and Michigan don't have many native earthworm populations and generally face more trouble.

"They change the soil structure by moving up and down the soil," Pinder said, adding that the movement causes water to penetrate deeper into the soil and away from plants that need it.

@NollyDak