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.”
