Once-plentiful populations of mammals are disappearing from the Florida Everglades, and wildlife experts think Burmese pythons are to blame. The giant, non-indigenous snakes can exceed 12-feet in length and are free to roam the swamplands without any natural predators. How bad is the damage? Here's what you should know:

What kind of animals are disappearing?
All kinds. Michael Dorcas, a biologist at Davidson College in North Carolina, wanted to see "how big a bite the pythons are taking out of the mammal population" in the Everglades, says Christopher Joyce at NPR, so he compared current day sightings of several animals with sightings from the 1990s — "when pythons were less common." He found a 99.3 percent decrease in raccoon observations, a 98.9 decrease in possums, 94 percent less white-tailed deer, and an 87.5 percent decrease in bobcats. Rabbits and foxes, which were once commonly spotted, were nowhere to be seen. Biologists suspected the numbers would be grim, says Dorcas, but "we had no idea they were going to be this dramatic."

How did the pythons get there? 
Many of the first ones were former pets that were released by their owners, and others may have escaped from pet shops during Hurricane Andrew in 1992, says Matt Sedensky at the Associated Press. They have been reproducing ever since, and now "tens of thousands" of the pythons are thought to live in the Everglades, "where they thrive in the warm, humid climate." Since 2000, the National Park Service has caught 1,825 of the constrictors, which average 12 feet in length and are capable of swallowing animals "as large as alligators." 

How do they know the pythons are eating everything?
The declining mammal populations could be a coincidence, says Ed Yong at Discover, "but the numbers fit in both time and space." The mammals are more abundant in areas of the park where the pythons aren't as common. And the areas that have sustained the "greatest losses" are those where the pythons "first staged their invasion." Diseases can be ruled out since the mammals come from different species, and hunting is outlawed in Everglades National Park altogether. 

Has this ever happened before?
After World War II, the predatory brown tree snake was somehow introduced to the island of Guam. "It took more than 30 years to work out what the snake was up to, and by then it was too late for many species," says Yong. Several indigenous species — such as the Guam flycatcher and rufous fantail — disappeared from the island completely. 

Is there any way to stop this problem?
Measures are already underway. In 2010, Florida banned private ownership of the snakes. And earlier this month, U.S. Interior Secretary Ken Salazar implemented a federal ban on the import of Burmese pythons along with three other snakes. 

Sources: Associated Press, CNNDiscover, NPR