Tom Rahill drives south, following a narrow road deep into the sawgrass marsh. On either side, clumps of trees can be seen dimly in the glow of a half moon. But Mr. Rahill keeps his eyes on the road, peering as far as he can into the tunnel of his headlights.
“You have to have your game on, otherwise you won’t get it,” he says. “You have to know what you’re doing.”
The air is warm and full of sounds – the whine of insects, and the squawk of birds, the incessant croaking of frogs. Small alligators lie on the road, soaking up the day’s warmth. As Mr. Rahill’s van approaches they raise their heads and scamper away. Coming upon a small, brown native snake slithering across the road, Rahill and his friend Ernesto Eljaiek, a Navy veteran dressed in heavy rubber boots and green fatigues, get out and gently carry it to the grass.
Their hunt is for another reptile – the Burmese python, which has become the poster snake for invasive species in the United States. First discovered here in Everglades National Park in the mid-1990s, pythons are thriving in South Florida. inflicting ecological damage on a scale that scientists say could be devastating. They are just one of the more than 50,000 invasive species in the US, plants and animals that came from somewhere else and are inflicting serious ecological and economic harm, according to a 2013 Congressional Research Service report.
There has been some progress in the fight against these invaders. Federal restrictions on ballast water from ocean-going ships seem to have reduced the number of exotic species getting into the Great Lakes. And scientists have developed new analytic tools to help them identify species that could pose an ecological or economical risk to the United States. The US Fish and Wildlife Service and the US Department of Agriculture are using these tools to prohibit the importation of some potentially harmful plants and animals.
But these efforts are not enough to keep many invasive species from finding a home and spreading. Along with Hawaii, the greater Everglades region is considered one of the most vulnerable ecosystems in the US to invaders.
“These reptiles in the Everglades are another example of how reacting is usually far less effective and more expensive than preventing species from being introduced and established in the first place,” says David Lodge, a professor at Cornell University and a leading expert on invasive species. “We know better. And government agencies and policymakers have begun to absorb the lesson.” But, he adds, “the rate at which policy has changed in reaction to invasions is much slower than the introduction of new species.
Gators by day, pythons by night
During the day, tourists at Shark Valley ride trams and bicycles along a 15-mile loop to see the sawgrass marsh and admire the alligators basking along the road. At night, it’s almost empty – except for the animals and, on this night, Rahill and Mr. Eljaiek. They are members of the Swamp Apes, a Miami-area group that Rahill started to help veterans help the Everglades. They hope to come upon a python slithering out of the marsh to cross the road.
If they do, they’ll stuff it in one of the king-sized pillow cases they carry in the back of their Honda Odyssey, stick it in an oversized cooler, and take it to a drop off point. From there a park employee will take it to park service lab, where it will be euthanized (using a stun gun like those used in slaughter houses) and dissected.
They make three circles of the loop road and see plenty of animals, but no pythons. It’s close to midnight. They’re weary. But Rahill is determined.
“You’ve got to just persevere, man,” he says. “You got to keep going.” The air has cooled, he notes. “This would be a good time for pythons to come out.” They go around once more.
Scientists believe the pythons got their start in the Everglades when local owners, alarmed at how big their pet snakes were growing, let them go in the wild. Native to southeast Asia, the snakes are big – the biggest found in the Everglades was 16 feet long and weighed more than 100 pounds. They are also very hard to find. But by 2000, it was clear the pythons were reproducing in the park. In 2012, the U.S. Fish and Wildlife Service placed the Burmese python on its list of injurious species, effectively prohibiting anyone from importing them into the US or transporting across state lines. But by then it was years too late.
“We’ve missed our chance,” says Tylan Dean, chief biologist at Everglades National Park. “We have pythons and very few people hold out strong hope that we can significantly reduce the python population in the future.”
The snakes have spread quickly across south Florida, expanding west to the Gulf of Mexico and north to where the sawgrass marshes and cypress swamps give way to tomato farms, citrus groves, and sugar cane fields. No one knows for sure how far they might spread.
“Maybe they’re not going to reach Washington, D.C., but they’re surely not going to stay in South Florida,” says Frank Mazzotti, a biologist and invasive species expert at the University of Florida in Fort Lauderdale. “Their range is going to expand.”
Their eating habits pose the biggest threat to the Everglades ecosystem. Pythons are constrictors: They kill their prey by squeezing it. And they hunt a wide variety of animals: birds, mammals, and even alligators. A study by Michael Dorcas, formerly a biologist at Davidson College in Davidson, N.C., found that in some some places pythons had devoured nearly all the mammals, including raccoons, marsh rabbits and even deer.
“We were amazed,” he says. Today in the Everglades, animals like the marsh rabbit, once abundant along the park’s roads, are almost never seen.
Quicker on the draw
But Mr. Dorcas’s findings raise still more questions. If pythons devour all the small mammals, will they turn to eating more birds? What happens to animals further down the food chain? And what will the consequences be for the Everglades’ other major predators – alligators, panthers, and bobcats – that eat many of the same animals as the pythons?
“It really becomes chaotic,” Mr. Dean says. “It’s very hard to predict.”
One consequence of the python invasion has been that local scientists and land managers are much more alert to new threats. Indeed, they say the pythons may not even be the biggest problem for the Everglades. Attention has recently shifted to Argentine black and white tegus, lizards that grow as long as five feet and eat just about anything. The tegus, which are known as as intelligent and affectionate pets, are also are in the wild and have adapted remarkably well to the swamps and marshes of south Florida. They haven’t colonized the Everglades, but they are very close, and officials are trying to stop them.
On the same day that the Swamp Apes hunt pythons at Shark Valley, Michelle Collier and Katie Sykes of the US Geological Survey drive along the Parkline Canal, just outside Everglades National Park, checking a line of tegu traps. The canal cuts a straight line across the sawgrass marsh and is part of a vast system of canals that drain much of the water that feeds the Everglades. The traps – metal Havahart traps that a homeowner might use to catch a raccoon – lie hidden in the brush just off the Parkline and other canals. Each is baited with a boiled chicken egg and shaded with a palm frond.
The two researchers say they often catch one or two tegus a day. They take the animals back to their lab to dissect. On this day their traps catch a box turtle, but no tegus. Despite the trapping, they say, they haven’t seen a drop in numbers. In fact, they say, there seem to be more tegus than ever.
“Once they’re here, it’s really hard to get them out,” says Ms. Collier.
That’s especially true in South Florida, where the subtropical warmth makes it hospitable to many plants and animals that can’t survive winter freezes farther north. Miami, which sits at the edge of the Everglades, is a convenient entryway for exotic plants and animals, with a busy international airport and a thriving trade in exotic pets and tropical plants. Along with Hawaii, the greater Everglades region is considered one of the most vulnerable ecosystems in the US to invaders.
Scientists haven’t given up on the pythons. Although they believe the snakes are in Florida to stay, they hope to limit the damage they inflict. Researchers are exploring a range of weapons used against invasive species, such as attractive pheromones, genetic manipulation, and parasites. They are also working to better understand the snake’s habits.
“We need to learn more about these animals, to find a weakness in their armor, some vulnerability that we might be able to exploit,” says Ian Bartoszek, a biologist with the Conservancy of Southwest Florida, who captures pythons on Florida’s west coast and dissects them at his lab in Naples.
In the meantime, ordinary citizens like Rahill and the Swamp Apes continue to fight what Mr. Mazzotti calls “the ground war” against the pythons--removing whatever snakes can be found. It’s not very effective--the number of snakes caught this way make little dent in their numbers--and it’s certainly not easy. On this night no python crosses their path.
But Rahill is loathe to give up. He lingers, and before heading home he hears something. He shines his flashlight into a bush, reaches in, and snatches up a small frog. The frog’s eyes shine in the light. It’s a Cuban treefrog, he explains, a small unassuming amphibian that was introduced to Florida in the 1920s and that has quietly spread across the state. In some places it’s completely displaced native tree frogs.
“We’re not ever going to run out of things to do,” he says--“even if we get the pythons under control.”