for National Geographic News
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In February, a group of tourists at the Pa-hay-okee Overlook in Florida's Everglades National Park stumbled upon a battle between an alligator and a python. The stunned onlookers watched as the snake wrapped itself around the alligator, only to see its opponent counter by rolling over and grabbing the snake in its mouth and swimming off with the snake in its jaw.
It was not the first such battle. In January of last year, a horde of tourists watched another epic contest between an alligator and a python at the park's Anhinga Trail. After more than 24 hours in the jaws of the alligator, that snake broke free and moved off into the marsh.
For now, the alligators in the Florida Everglades are holding their ground against the invading snakes. But the odds may be changing. The park is being overrun with Burmese pythons, one of the world's largest snakes. These pythons can grow to be more than 20 feet (6 meters) long in their natural habitat in Southeast Asia.
The Burmese python is just one of thousands of non-native animal and plant species that have invaded the United States in the last decades. Florida teems with exotic creatures that have no business living there. Other regions have their own problems. Snakehead fish, for example, have infested the Potomac River near Washington, D.C.
The economic toll from damage by invasive speciesand the costs of trying to control themis enormous: U.S. $137 billion a year, according to a 1999 Cornell University study.
The ecological outlook is equally grim. Second only to habitat loss, invasive species are a leading cause of species endangerment and extinction both in the United States and worldwide. Almost half of the species on the U.S. endangered species list are threatened wholly or partly by introduced species. Steven A. Williams, director of the U.S. Fish and Wildlife Service, calls invasive species the number one environmental threat to the United States.
Not So Cute
Some invasive species may be "stowaway" organisms that arrive here inside packing materials, or micro-critters that are dumped from ships' water tanks. But many plants and animals also enter the U.S. as part of the booming trade in exotic pets or food.
Burmese pythons are popularand legalpet snakes. In the past five years, the U.S. has imported more than 144,000 Burmese pythons. Hatchlings sell for as little as U.S. $20. But once the cute little baby snakes turn into 15-foot-long (5-meter-long) beasts, some owners may decide to get rid of their pets by dumping them in the forest.
"All of the Burmese pythons that we see in the park are a product of the international pet trade," said Skip Snow, a wildlife biologist at Everglades National Park.
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