Unwanted guests: invasive species, ranging from mussels to weeds, are costing the country billions.

• Author: Farquhar, Doug

On a sunny day in the early spring of 2004, friends of Michigan Senator Patricia Birkholz took their 20-foot speedboat for a cruise in Lake Michigan. They were two to three miles off the coast when their motor seized. Mechanics later found why the engine had failed--the entire motor intake was full of zebra and quagga mussels that have spread throughout the Great Lakes in the last 20 years.

The mussels are just two of some 50,000 invasive species that have found their way into the United States. They include foreign plants, animals and microorganisms that spread quickly and aggressively, competing with native plants and animals. Global trade exacerbates the problem, with species hitching rides on cargo destined for U.S. ports.

Exotic species alter the ecosystem by changing the food chain, reducing biodiversity and upsetting ecological life cycles. They can transmit foreign diseases or parasites, clog water intakes, push out helpful species, and cause brush fires to spread easily.

Invasive plants already have taken over more than 100 million acres, from open spaces in the suburbs to pristine mountain meadows in our national parks.

The federal government has invested millions to curb the spread of these unwanted species, but it's losing the battle.

Some state lawmakers are frustrated by the ineffective federal effort. They want bolder action. All 50 states have passed legislation to combat invasive species, and 25 states have invasive species coordinating councils. In 2009, legislatures in 40 states considered more than 180 invasive species related bills, and 64 were passed. They addressed everything from wild boars to boll weevils.

"States have to take leadership on this issue because different invasive species are going to affect states differently," says Minnesota Representative Rick Hansen. "We have different ecosystems, and some are more susceptible to pests than others.

"In Minnesota, we have a significant population of ash, so we have a real threat from the emerald ash borer as it moves west. States can work in partnership with the federal government, but states need to take leadership because threats are different."

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MASSIVE COST

The cost of invasive species in the United States is estimated at more than $120 billion annually. One study estimates annual losses to crops at $13 billion, grazing areas for livestock at $1 billion, and forests at $2.1 billion.

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Agriculture...