Fast-growing hordes of invaders are crossing the nation's borders by land, sea and air and threatening to devastate the economy, spread contagion and wreak havoc on the environment.
That could be a science fiction plot if it weren't for the most part true. Thousands of invasive plants, animals, bacteria and viruses cause major problems across the country and cost an estimated $137 billion in damages every year, according to the National Governors Association.
Known by colorful names such as the snakehead fish, the emerald ash borer, the rusty crayfish and "rock snot" algae, they can arrive from overseas as exotic pets, as specialty foods or even unwittingly shipped in the ballast water of ocean liners. Boaters and fishermen also can carry invasive species across states lines in bait buckets or on the hulls of their watercraft.
In a new environment, a foreign species may have no natural predators and multiply quickly, gobble up food sources or native animals or spread disease to livestock, and even humans.
Emerald ash borers have killed 20 million trees in three Midwestern states. Tens of thousands of chickens were killed after a 2004 outbreak of avian flu, which can be spread by wild birds. Up to 40 percent of the animals on the U.S. lists of threatened and endangered species are at risk because of non-native animals, according to the environmental advocate group Defenders of Wildlife. More than 80 percent of stream and river miles in Arizona, Colorado and Montana contain foreign species that negatively impact the native animals. In November, tiny zebra mussels were blamed for shutting down a nuclear power plant in New York.
State and federal governments are fighting back by laying traps, building underwater barriers or spreading poison. But their best bet is taking preventive measures.
Oregon environmental officials have set up a phone hotline, 866-INVADER, for callers to report animal invaders. A Michigan law that took effect this year is the first of its kind to prohibit oceangoing ships from dumping untreated ballast water, which could carry unwanted creatures.
At the federal level, a bill in the U.S. House of Representatives would provide states with matching funds to eradicate destructive species and protect native plants and animals. The U.S. Senate also is considering a bill to regulate ballast water. But states oppose it because it prevents them from setting tougher standards and also removes ballast water from regulation under the federal Clean Water Act.
"The Great Lakes are our most precious natural resources, and aquatic nuisance species are among the most serious threats to their health. The (Environmental Protection Agency) needs to enforce the Clean Water Act, and Michigan's ability to protect the Great Lakes should not be pre-empted," said Michigan Attorney General Mike Cox about his September letter to Congress that was co-signed by attorneys general in Illinois, Minnesota, New York, Pennsylvania and Wisconsin.
While there is now growing attention to the problem, non-native animals have a long history of taking over new territories. Rats and other animals brought to the island of Mauritius by 17 th century Dutch explorers are commonly blamed for the extinction of the flightless dodo bird.
Media reports in recent years have highlighted the migration of creatures that seem to defy nature, such as the snakehead , a voracious fish that can wipe out competing species, briefly survive out of water and even crawl short distances across land.
Maryland wildlife officials poisoned a pond in 2002 to kill off snakeheads that were making their way into the Potomac River that borders Washington, D.C. In 2004, another Maryland pond was drained and dredged to remove the so-called "frankenfish" brought from Asia for aquariums and specialty food markets.
The snakehead is one of an estimated 2,240 species of live, wild animals legally imported to the United States between 2000 and 2004, making the country the world's largest market for live animal imports, according to a study by Defenders of Wildlife. Live animal imports are regulated by the U.S. Department of Agriculture.
The environmental group concluded that 302 of those species have the potential to "cause environmental disruption, economic harm or threats to human and animal health," including the Indian mongoose, which eats eggs of endangered birds in Hawaii, and the profligate Burmese python eating its way through the Florida Everglades.
Defenders of Wildlife is pushing for greater restrictions on live animal imports, which also are responsible for introducing foreign diseases that infect wildlife, livestock and even humans. One example is the 2003 outbreak of monkeypox, which infected several people and prairie dogs before it was eradicated. The virus, which causes a fever and rash but is rarely fatal, was carried to this country by Giant Gambian rats from Africa.
An unlikely but much more serious threat from animal imports is the deadly avian flu strain, H5N1, which could cause a pandemic killing millions worldwide by some estimates. In response to the danger of avian flu, the United States should follow the example of the European Union, which has banned all live bird imports, said Defenders' researcher Peter Jenkins.
Other strains of avian flu have infected North American poultry several times in recent years, including a 2004 outbreak at live-bird markets in New Jersey and farms in Delaware, Maryland and Texas, according to the national Centers for Disease Control and Prevention. Two Canadians were infected with an avian flu strain after a 2004 outbreak, and a New York patient was found to have avian flu in 2003, according to the CDC.
Unwanted critters also are introduced accidentally, as in the emerald ash borer , a beetle discovered in the Great Lakes region in 2002 that probably arrived in ash-wood packing crates on cargo ships, according to the Michigan Department of Natural Resources. Larvae of the ½ inch-long beetle are blamed for killing 20 million ash trees in Indiana, Michigan and Ohio.
As a result, state and federal officials caused a quarantine of ash wood in those states and in Illinois, Maryland and Pennsylvania, as well as the destruction of perimeter forests around infested trees. Studies also are under way to see whether natural enemies such as a stingless wasp, a predator of the borer, could be used to control it.
In the case of another invasive species, the zebra mussel , officials learned that size doesn't matter. These fingernail-small shellfish likely were carried in ballast water from the Caspian Sea to the Great Lakes in the late 1980s. They have spread rapidly through the region's waterways and are blamed for contributing to the shutdown of an 850-megawatt nuclear power plant in Scriba, N.Y.
The mussels eat other free-floating algae, which helps seaweed grow more quickly in Lake Ontario from which the power plant draws water. The abnormal amount of seaweed eventually clogged an intake pipe from the lake to the power plant.
Zebra mussels were found this year in lakes that supply drinking water to St. Paul, Minn. They are not a hazard to humans nor to water quality but can clog screens, valves and intake pipes. Once they are established, they are impossible to eradicate without harming other species at the same time, according to the U.S. Interior Department.
Even species from other states can cause problems when they are released into a new habitat. The " rusty crayfish ," described as the king of all crawdaddies, has devastated local aquaculture in 14 states outside its native Ohio River Valley, according to the Maryland Department of Natural Resources.
Maryland officials discovered the creature in state streams during the summer and are concerned that it will destroy endangered freshwater mussels. Fisherman use the crayfish as bait, and the state is now fining sportsmen at least $125 if they are caught dumping bait buckets with exotic species into streams.
Fishermen and boaters across North America also are spreading the so-called "rock snot" algae, didymosphenia geminata , which smothers other species with a thick carpet of blooms. The freshwater alga were originally discovered in Scotland, parts of Scandinavia and parts of China in the late 19 th and early 20 th centuries. Now its range is rapidly expanding southward to new areas of North America and also in Europe and New Zealand.
In this country, states are helpless, so far, to stop its spread, except to advise sportsmen to clean their boats and fishing gear with bleach or a salt solution.