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Could alien earthworms damage U.S. ecology?

By Brad Haire
University of Georgia

When they do what they do best, they can help farmers raise healthier crops. But at the same time, they could be doing harm. Most of the ones you see are probably aliens. But one thing's for sure, they're great fish bait.

Earthworms are among the most important animals that live in soils, says Paul Hendrix, a crop and soil sciences and ecology professor with the University of Georgia College of Agricultural and Environmental Sciences.

Soil eaters

As earthworms munch through the soil, they aerate it and leave behind fertile droppings. "Soils with a lot of earthworms crawling around are generally considered good for agricultural systems," Hendrix said.

The most familiar earthworms are 8 to 10 inches long. But earthworms aren't all alike, he said.

There are 3,500 earthworm species in the world. North America is home to about 150. Of these, about 45 are exotic, European species introduced on purpose or by accident by colonial settlers. The earthworms probably tagged along in soils used to ballast ships or carry plants.

New digs

These subterranean immigrants, much like the immigrants that brought them, found this new world welcoming.

It appears, Hendrix said, that the dominant nonnatives have replaced most of the native species in the developed parts of United States. Most earthworms found in lawns, the woods near homes or in fields are exotics.

Most native species don't like the way humans tend to disturb the soils where they live and work. But the exotics don't mind at all.

"These earthworms really thrive in human-modified environments all over the world," he said.

Invaders

Most of the European species -- again, like the Europeans who brought them -- are naturalized citizens by now. But that doesn't mean they're safe.

Are they doing any unseen harm to the U.S. environment? And, if other foreign species are introduced, could they cause harm in the future?

It's happened in the past. An animal, plant, bug or fungus that's harmless in its native land can bring disease or other problems to another country. And with the new global economy forcing countries into more direct contact, damaging exotic earthworm invasions are even more likely.

For example, scientists believe earthworms can carry foot-and- mouth disease, a devastating livestock disease. And the voracious appetites and burrowing habits of foreign earthworms have thinned forest leaf litter in areas of Minnesota, threatening plants that depend on the leaf litter.

The U.S. Animal and Plant Health Inspection Service is considering guidelines to regulate the introduction of exotic earthworms into the United States.

Hendrix is one of a handful of scientists studying the characteristics of exotic earthworms in America, the geographic extent of their invasions, how they do it and what damage or benefit they could provide below- and aboveground.

He's studying earthworms in Florida, North Carolina and Oregon. He published an article about the possible ecological and policy implications of exotic earthworm invasions in the September 2002 issue of "BioScience."

(Brad Haire is the former news editor with the University of Georgia College of Agricultural and Environmental Sciences.)

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