Keeping foreign critters at bay

"Everybody's having this problem," he says, noting similar challenges in Australia, Africa, and Europe, where shipments of US corn to the Balkans in the aftermath of the Bosnian crisis apparently carried insect pests that have gained a foothold in some eastern European countries, threatening their corn crops.

"We're playing ecological roulette," warns James Carlton, a marine scientist at Williams College in Williamstown, Mass., and editor in chief of the journal Invasion Biology.

While the northern snakehead has become the latest poster child for invasive species in the US, other invasive species have been making headlines this summer, including:

• the emerald ash borer, a beetle native to Russia that is destroying ash trees in Michigan, Indiana, and may be working its way into Ohio. The borer is thought to have arrived in packing material protecting a shipment of bulk steel from Russia.

• three species of Asian carp, which are heading up the Chicago Ship and Sanitary Canal toward the Great Lakes. The carp were originally imported to control algae and shellfish on fish farms in the South. These fish could seriously damage, or even destroy the Great Lakes ecosystem, researchers say, because each female carries as many as 1 million eggs, and adults consume up to 40 pounds of plants, plankton, or shellfish daily.

• Japanese shore crabs, which this summer have been spotted near Maine's Penobscot Bay, the northernmost sighting along the East Coast. These tiny crabs are partial to clams, mussels, and lobster – the heart of Maine's shellfish industry.

• giant hogweed, a member of the carrot family that grows up to 20 feet tall. Native to the Caucasus Mountains and southwestern Asia, the plant was imported as an ornamental, but quickly spread. The plant, newly spotted in western Massachusetts, is considered a potential public-health hazard because its sap sensitizes skin to ultraviolet radiation, according to state environmental officials.

Indeed, biologists who focus on invasive species can tick off a long list of other species that need to be controlled.

"One of the great lessons of invasion ecology that surprises us again and again is what species will do in an environment where they did not evolve," says Dr. Carlton.

Australia and New Zealand have become what MacIsaac calls the "world leaders" in identifying potential invasive species before they arrive. Using statistical techniques and computers to make the comparisons, Australia has developed a database of 300 species and their characteristics to determine which will be let into the country.

So far, MacIsaac says, the invasion model is showing an 88 percent accuracy rate.

"It's so difficult to deal with species after they get in that you have to go to prevention, prevention, prevention," Carlton says.

"Still," he adds, "I am optimistic." He cites a range of examples where agencies, both local and international, are becoming more proactive in confronting invasive species.

Adds MacIsaac, "We've got to be vigilant."

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