The silent invasion 

Six-hundred miles west of Rochester, in suburban Chicago, is a structure that just might save Lake Ontario.

Connecting the Chicago and Des Plaines Rivers, the Chicago Ship and Sanitary Canal links up two of the continent's largest water systems: the Mississippi River and the Great Lakes watersheds. At the bottom of that canal lies a $9 million underwater electric fence that's keeping species on one side from migrating to the other.

Specifically, Asian carp. Brought to this continent in the 1970s by catfish farmers, they escaped during floods, spreading throughout the Mississippi River and its system of tributaries. A bigger, badder version of the homegrown carp we always had, these fish can grow up to four feet and 100 pounds according to the federal Environmental Protection Agency. And their ability to leap up to six feet out of the water --- often frightening and sometimes injuring fisherman and biologists --- has garnered plenty of headlines.

The fish are already thriving in the Mississippi system and nearly everyone is petrified about the possibilities if they reach the Great Lakes.

"Due to their large size, ravenous appetites, and rapid rate of reproduction, these fish could pose a significant risk to the Great Lakes Ecosystem," the EPA's website reads. "Eventually, they could become a dominant species in the Great Lakes."

But Asian carp are just one of an estimated 50,000 species from beyond our shores who've taken up permanent residency here. And some of them are costing us. David Pimentel, a professor of entomology at Cornell University, estimates that those species suck more than $125 billion from the economy. Much of Pimentel's recent research has focused on "aquatic nuisances," an appellation that covers a broad range of species. In New York alone he estimates aquatic invasive species cause about $500 million in damages by creating problems like clogged pipes or choking off waterways.

"That does not really include terrestrials," says Pimentel. "I would say probably the rest would be about $3 billion."

Some of these are infamous enough to be widely recognized --- zebra mussels, Asian longhorn beetle, purple loosestrife.

But others are less obvious. Asked what the single most costly invasive species was, Pimentel paused a moment before fingering the HIV virus, followed by the West Nile virus.

And 73 percent of the agricultural crops used in North America are invasive, he adds. Now those plants are struggling to cope with newer forms of invasive plants, in other words: weeds. About 12 percent of crop production is lost to weeds each year nationally, says Pimentel. For New York, that means $300 to $500 million dollars gone from the pockets of the state's already struggling farmers. Other plants, like purple loosestrife --- the flower you see in ditches, medians, and roadsides throughout the state --- cost local governments money to keep (at least partially) under control.

For Pimentel, weeds and other introduced plants are the worst part of the problem. In addition to the economic harm done to farmers, landowners, and governments, there's the less quantifiable specter of extinctions.

"Invasives cause 40 percent of extinctions in the US," says Pimentel. That's second only to those caused by human activity. And invasive plants that out-compete native species can have an extinction multiplier effect. That's because plants are the foundation of the food chain; tear them out of the equation and ecological relationships higher up will topple. Pimentel explains: "Any time you have a plant that's headed for extinction, you have the extinction of a lot of the species that are dependent on that plant."

These days, when it comes to fighting invasive species, the outlook is grim. Since the mid-20th century, there's been an explosion of new species here.

"I think we should be worried about this because it's rapid and increasing," Pimentel says. "In just half the time, the number of species coming in has more than doubled. Evolution in natural systems can't happen fast enough to adapt to that."

The blame for that, Pimentel suggests, lies with the rapidly changing nature of the global economy.

"We've got more people traveling, traveling more rapidly, and we've got globalization and increased trade," he says. And our track record of stamping out the invasives we've fought thus far is miserable.

"Out of those 50,000 species, we've eradicated maybe two," he says.