Huge, Freed Pet Pythons Invade Florida Everglades

Stefan Lovgren
for National Geographic News
June 3, 2004
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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 species—and the costs of trying to control them—is 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 popular—and legal—pet 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.

Snow's office voice mail also doubles as a python sightings hot line. Since the mid-1990s park rangers have captured or killed 68 Burmese pythons in Everglades National Park.

The pythons are now most certainly breeding in the park. They have been found eating gray squirrels, possums, black rats, and house wrens. Perhaps even more worrying, the pythons may be preying on native mangrove fox squirrels and wood storks. And they could be competing with the eastern indigo snake for both prey and space. The eastern indigo snake is listed as threatened by the U.S. Fish and Wildlife Service.

There are serious concerns about human safety as well.

Florida teems with other non-native species—from African monitor lizards to vervet monkeys. "Its diverse habitats and suitable climates from the subtropical southern peninsula and Florida Keys north to the subtemperate panhandle have facilitated exotics in becoming established and expanding their ranges," said Kenneth Krysko. Krysko is a herpetologist at the Florida Museum of Natural History at the University of Florida in Gainesville.

Experts say the greatest damage from invasive animals may be done by aquatic species. Earlier this year a survey revealed that 16 species of non-native tropical fish have been found at 32 locations along the southeast coast of Florida—all most likely introduced when hobbyists freed aquarium fish into the ocean.

Too Slow to Act

But Florida is hardly alone in the fight against invasive species.

The emerald ash borer first arrived at a Great Lakes port in wooden packing material on Korean or Chinese freighters a couple of years ago. Since then the metallic green Asian beetle has destroyed six million trees in Michigan.

San Francisco Bay contains some 260 non-native species. The African clawed frog, meanwhile, has taken over Lily Pond in San Francisco's Golden Gate Park. Native to Kenya, the frogs eat almost anything and breed like crazy. They alter ecosystems by gobbling up insects, fish, and even birds. The only way to prevent them from spreading is to kill them, but that would cost cash-strapped California millions of dollars.

Many experts say the United States has been too slow to act and is now paying the price.

"Once these invasive species are established, they are virtually impossible to eradicate," said Ken Burton, a spokesman at the U.S. Fish and Wildlife Service. "In most cases we can only hope to control them."

Dean Wilkinson, the invasive-species coordinator for the National Oceanic and Atmospheric Administration in Washington, D.C., says a new approach is long overdue.

"In the past we treated this as individual pest problems," Wilkinson said. "It's only recently that we've recognized this as a major environmental and economic problem. If we had had the foresight to spend money at the front end, we would not have had to spend millions to deal with the problem at the back end."

Biological Pollution

It's not just animals but also plants that cause damage. According to the United States Department of the Interior, 100 million acres (40 million hectares) of land in the U.S. are infested with invasive plants.

"The invasive species having the biggest ecological and probably economic impact are those that modify habitat," said Daniel Simberloff, a biology professor at the University of Tennessee in Knoxville. "Most of these are plants, like melaleuca and Brazilian pepper in South Florida, or cheatgrass in the West."

Increased global travel and trade have exacerbated the biological pollution. The booming trade in exotic animals as pets has opened the floodgates for invasive species coming into the U.S. Miami International Airport reportedly receives 70 foreign shipments per day, some with thousands of animals, such as tarantulas, lizards, and snakes.

Many of the species are illegally imported. Only 1 to 2 percent of cargo containers are actually opened and checked. But many of the exotic animals are perfectly legal to bring into the country. U.S. residents, for example, can legally own 22 of the 24 pythons found around the world.

"As the trade expands, the problem of invasive species will become worse," Burton said.

Snow, the Everglades National Park biologist, appeals to pet owners who may have grown tired of their exotic animals: "Please don't release them into the wild."

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