The Conqueror Earthworm
In the scientific community, concern over the depredations of invasive earthworms has been growing for years. The International Symposium on Earthworm Ecology has been meeting every four years since the 1970s, and earthworms will also be a focus of a meeting of the International Colloquium on Soil Zoology and Ecology in Rouen, France, this summer, said Paul Hendrix, a professor at the Institute of Ecology at the University of Georgia.
"We're starting to see pretty dramatic effects now, especially in the northern regions of North America, where there weren't already worms," Hendrix said. "Ferns and other understory vegetation are being threatened by changes in the forest floor."
In woodlands in the Chicago area, where Heneghan and Steffen are doing their research, the invasive earthworm problem involves another invasive species -- buckthorn. Buckthorn is a thick, hardy shrub native to Europe that was brought to the Midwest in the 1880s for landscaping. It flourished in midwestern forests, depleting the indigenous oak and other native species.
The invasive European earthworms love the buckthorn detritus, and buckthorn thrives on the extra nitrogen that earthworms create in the soil.
"There's a symbiosis between the European earthworms and European buckthorn," Heneghan said. "Together, they're creating great mischief."
Steffen and Heneghan are measuring the density of earthworms in the soil in McDonald Woods and other forest preserves in the Chicago area. To quantify the worm population, they drive a square, open-bottomed steel frame, measuring about a foot on each side, into the earth and saturate the soil with a mixture of organic mustard and water that irritates the worms' skin. That brings the worms to the surface, where they are collected and counted.
"When the big night crawlers come out, it's like watching a submarine surface," Steffen said.
The earthworm study goes hand in hand with efforts to restore the area to its natural oak habitat. This slow process is the best way to combat the earthworm problem, the scientists said.
"You could fumigate the soil, but we don't want to do that because that would also have an effect on non-target organisms," Heneghan said. "The worms don't have a taste for oak leaves."
Steffen and Heneghan said raising awareness about the problem is a good way to educate the public about the issue of invasive species and their effect on fragile, interconnected ecosystems.
"You have a much more difficult time talking to people about buckthorn -- it's just a bush," Steffen said. "But when you slap an earthworm in the face, it gets everyone's attention."
© 2004 The Washington Post Company