Fight against non-native animals, plants is often a delaying action

By David Zizzo

Published: August 5, 2008

They come on the wind, in the water and on the ground. They sneak across borders, cling to trucks and stow away in home appliances.

Invasive species of all kinds — plants, insects, birds, mammals and others — are on the attack around the world, depending on your definition of "attack.” Any species that's not native to an area, scientists say, is considered invasive, a definition that, depending on how you look at it, could even include those of us at the top of the food chain.

Some invasive species blend in and find niches, even having positive influences. For instance, pheasants are popular among hunters in western Oklahoma, said Nels Rodefeld, spokesman for the state Wildlife Conservation Department. Also, striped bass have become an industry since being intentionally introduced into Oklahoma lakes and rivers.

"Technically that fish is a non-native,” Rodefeld said.

Other invasives, however, can wreak environmental havoc or cause billions of dollars in damage.

"Invasive species in general is a gigantic problem in a lot of places,” David Britton said. As aquatic nuisance species coordinator for the U.S. Fish and Wildlife Service's Region 2 in Dallas, Britton is concerned about invaders such as the notorious zebra mussel. Since their introduction to the Great Lakes from international cargo ships, the prolific critters have spread into waters across the eastern U.S., including parts of Oklahoma. They can clog intakes for cooling water for power plants and can damage boat engines.

Introduced in the 1970s by fishermen to control algae in catfish farms, Asian carp can grow to 100 pounds and have infested rivers in the Northeast.

"The carp actually jump out of the water,” Britton said. "People up there go bow-hunting for them while they're in the air.”

Other aquatic invasives include plants such as Eurasian water-milfoil, a plant that flourishes in nutrient-rich waters, including those in Oklahoma, clogging lakes and rivers as it spreads.

Despite efforts to prevent the plant's spread, all it takes is one fisherman carelessly moving a boat to introduce the invader to another body of water, Britton said. "People can come out and do something that will literally cause a billion dollars of damage, and they don't know or care.”

Some invasives survive because they are more aggressive or are more successful at reproducing, such as the English sparrow and the European starling, which displace native species. Of course, birds fly, and when they do that over long distances as part of their natural life cycle, it's called migration rather than invasion.

Most invaders have an advantage, said Richard Grantham, entomologist at Oklahoma State University. "Because they are invasive, they don't have natural enemies here.”

Some invasives have flourished because of civilization, which ironically is now trying to rid itself of the invaders. An example is the eastern red cedar, which sucks up valuable water and provides little agricultural value. "Cedar didn't live on the plains because the plains burned up every few years,” Rodefeld said.

Some invasives hitch rides aboard various modes of transportation or migrate distances on their own, such as fire ants, Africanized bees or Formosan termites. Or "crazy” Rasberry ants, insects first spotted in California in 2002 that seem to have an appetite for electrical components.

About 2.4 percent of land in the National Wildlife Refuge System is infested with invasive plants. And 4,400 invasive animal populations occupy refuges, the U.S. Fish and Wildlife Service reported. The global economy — and the industriousness of invasives — have helped spread them. Cargo ships bring in shipping containers and pallets that can hide numerous species, and they dump ballast water that can carry others.

Some have even been known to hole up in the belongings of American military members returning home, Britton said. "Things like brown tree snakes are really good at hiding,” he said. "They're commonly found in washing machines.”

We're not totally powerless against the invaders, experts say.

Officials eradicated furry nutria from the Blackwater National Wildlife Refuge in 2004. Biologists plan to rid Rat Island of the critters that gave the Alaskan island its name, rodents that have ravaged the island's seabird population after a Japanese ship ran aground there 200 years ago.

However, in many cases, such as invasions by zebra mussels and many plants, the best we can do is try to slow their spread, maybe buying time until technology can find new weapons, experts say.

"Once you have them, there is no cure,” Rodefeld said. "There's only management to slow down their spread or minimize their impact.”

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