Wildlife experts are accusing the U.S. government of failing to adequately control the imports of exotic pets sold online. A Cornell University study shows that these animals cost the U.S. economy $138 billion a year in spending to manage invasive species, lost agriculture and forestry production, and declining tourism revenues in impacted areas. Steve Mort reports from the Everglades National Park in Florida, which has seen a dramatic rise in one particular invasive species.

It is a Burmese python that Albert Killian from the Everglades Outpost wildlife refuge is showing off. He says these snakes can reach six meters long, weigh as much as 90 kilograms and live up to 25 years. "South Florida is a perfect habitat for them. The conditions here simulate the conditions of their natural habitat so the snakes will thrive here in south Florida".

The local Fish and Wildlife Commission believes pet importers introduced Burmese pythons to the U.S.  Many were abandoned, joining hundreds of non-indigenous species already in Florida.

Albert Killian says Burmese pythons are now firmly entrenched among the 50 reptile species found in the Everglades, and it is now simply a case of trying to manage them. "The problem extends to the point where you can't fix it -- all you can do is control it -- meaning, the snakes are out there to stay. There's no way they're ever going to get rid of them."

Although the South Florida Water Management District says 170 Burmese Pythons were killed in 2006, the snakes can lay as many as 100 eggs at a time, so their numbers continue to rise.

Conservationists say the snakes threaten many indigenous animals.

And scientists have found numerous species inside Burmese Pythons, including endangered bobcats. In 2005, the National Park Service released a picture of a snake that exploded while swallowing an alligator.

Wildlife biologist and alligator expert, Joe Wasilewski, says the snakes are the first real threat to Florida's alligators. "If these pythons get a good taste of alligator -- small alligators -- and like it, they can certainly, in the future, put a good dent in the alligators' population. That's certainly feasible."

Wasilewski, says up to 500 Burmese pythons have been captured in south Florida in the last two years, and the U.S. National Park Service estimates there are roughly 5,000 in the Everglades.

State lawmakers passed a bill in April making it a crime to release pythons into the wild. University of Florida scientists are using radio transmitters to track the snakes, and nine local agencies have formed a working group to tackle their spread.