Invasive Pythons Put Squeeze On Everglades' Animals

toggle caption Joe Raedle/Getty Images

Scientists are reporting that aliens are wiping out the animals in Florida's Everglades.

The aliens are Burmese pythons from Asia. They've been slithering around south Florida for decades. But scientists now say the constrictors are so bad, they're eating their way through the swamps. And the federal government has decided to take action to prevent their spread.

One scientist who has been trying to find out just how bad the invasion has become is Michael Dorcas. He's been catching snakes since he was a child in Texas. But he says a 15-foot Burmese python is a handful ... or two.

"You typically try to grab them behind the head," he says, and "get somebody else to grab the back end of them. But often they still defecate all over you, even if they can't bite you, so it's always an unpleasant thing when you catch a wild python."

Dorcas is now a biologist at Davidson College in North Carolina. For the past eight years, besides catching pythons, he has been driving through the Everglades counting animals — specifically, midsize mammals.

Dorcas wanted to know how big a bite the pythons are taking out of the mammal population. When he compared the number of mammals now with the 1990s, when pythons were less common, he was shocked. "Once we calculated the percentages, we had no idea they were going to be this dramatic."

How dramatic? "A 99.3 percent decrease in raccoon observations," he reports. "Decreases of 98.9 percent in possums, 94 percent white-tailed deer, 87.5 percent in bobcats."

Pythons Removed From The Everglades The chart below shows the number of pythons removed from the park and neighboring areas between 1995 and 2010. Researchers say the slight decrease in the number of pythons captured in 2010 might be the result of a severe freeze in January of that year.

Nearly all the raccoons, possums, deer and bobcats gone.

Now, counting animals by sight from a car isn't foolproof, but it is an accepted practice in wildlife research.

Dorcas reports his findings in the Proceedings of the National Academy of Sciences. He says it's the first study to actually quantify the effect of the pythons' appetite in the Everglades.

A Python Invasion

He blames pythons because in areas known to be thickest with the snake, the mammals are scarcer. Where there are fewer pythons, there are more mammals. And there's no evidence that a disease is to blame, either. Furthermore, mammals and birds (the latter are also common snacks for pythons, as necropsies have revealed) often gather near water, where pythons like to feed. And Dorcas points out that snakes big enough to eat a good-sized raccoon haven't lived in Florida for millions of years. So "local" animals are "naive."

The onset of the python invasion is often blamed on snake owners who release their pets when they get too big for comfort.

Lawyer Marshall Meyers represents the pet industry and the Pet Industry Joint Advisory Council. He says maybe some pet owners do that, but he also cites a report that a hurricane overwhelmed a snake breeding site in Florida that could have spread the snakes. And while pythons are no doubt eating mammals, it's more complicated than that.

"I think it's habitat loss," Meyers says, and the fact that there's less fresh water in the Everglades now, which could reduce wildlife numbers.

But he acknowledges that the python invaders and other exotic animals that escape or are released by owners give the pet trade a bad name.

"They're species that are not in this country, that we do not want in this country, because if they came in through pet trade or through the zoos, they can cause a lot of environmental harm, and that's just a big black eye," he says.

Enlarge this image toggle caption Lori Oberhofer/National Park Service Lori Oberhofer/National Park Service

A Ban On Importing Pythons

The U.S. Fish and Wildlife Service has been watching the python explosion and is taking action. On Jan. 17, the agency made it illegal to import Burmese pythons or transport them across state lines. That includes three other constrictor species from Africa and South America: the yellow anaconda and the northern and southern African pythons.

Biologist Susan Jewell, with the service, studies injurious species that invade the U.S. — things like zebra mussels and poisonous lionfish. She says it's possible Florida's pythons could spread if they learn how to survive in colder weather. "I think that it's a good heads-up for everybody," Jewell says. "This can happen anywhere — and most likely will if these snakes get established."

Jewell says invasive species sometimes thrive in new places where they don't have natural enemies. "It just shows what we don't know about species when they get taken out of their native range and taken to a new area," she says.

Jewell says the import ban won't help the Everglades — it's too late there. It's meant to keep pythons and other constrictors from spreading. The Fish and Wildlife Service's research suggests that they could live almost anywhere in the Southern U.S.

The ban allows people who now own these snakes to keep them, and you can still buy and sell them within a state or export them overseas. Jewell emphasizes that the new rule doesn't mean anyone has to give up his snake.