If you go down to the Florida Everglades today, you're in for a big surprise: in the past 12 years, 90 per cent of the wild mammals which once roamed freely through the National Park have gone.

Snakes are to blame, say scientists. Big ones. Specifically: an exponentially-growing population of Giant Burmese Pythons, which can grow up to 16 feet long and have a huge appetite.

The creatures were first discovered in the park in 2000. They got there after being released into the wild by overwhelmed pet owners, and quickly established a breeding population.

No-one knows exactly how large their population has grown. But in the past 12 years, rangers have captured or killed a total of 1,825, without seeming to make a significant impact on their ability to reproduce, voraciously. Now scientists have started measuring their impact. And the results are sobering: in areas where the snakes are well established, foxes and rabbits have disappeared. Sightings of raccoons are down by 99.3 per cent, opossums by 98.9 per cent, and white-tailed deer by 94.1 per cent.

A paper published * the proceedings of the National Academy of Sciences, claims pythons are also harming bird and coyote populations and threaten already-rare rival predatory species, such as Florida panthers, with extinction.