The Problem with Pythons

Burmese pythons are slowly, inexorably eating their way through Florida’s wildlife—is hunting them the answer?

On a windy evening in January, herpetologists David Steen and Sean Sterrett drove Steen’s dirty pickup truck to a meeting point on the shoulder of a South Florida road. Florida wildlife officials and volunteers waited on the grass, and when Steen and Sterrett popped open the bed of the truck and began pulling out a giant Rubbermaid container, a volunteer asked the two men, “So—is it dead, or alive?”

At the bottom of a white pillowcase tied shut at the top, and latched into the plastic bin was a very alive, and very large Burmese python. Just hours earlier, Sterrett had caught the outsized reptile as it skirted the edge of a muddy puddle that he thought might hold a python or two. When he grabbed it, the snake—nearly 10-feet long and thick in the middle—sank its teeth into Sterrett’s forearm and started to coil, first around his arm, then his leg. Sterrett was alone, ahead of Steen and their companions—and when the constrictor started going for his neck, it “scared the shit out of me,” he said. By the time he managed to wrestle the live snake into the sack, Sterrett was bleeding and reeked of the ammonia smell of snake musk.

This snake was the reason Sterrett, a herpetologist with the U.S. Geological Survey in Massachusetts, had flown down to Florida. He and three other snake-enthusiasts made the trip there for the 2016 Python Challenge, a competition to capture Burmese pythons (Python bivittatus)—exotic, non-venomous, semi-aquatic constrictors. These massive snakes that sometimes grow to more than 20 feet long are threatened in their native range of Southeast Asia, where they’re victims of habitat destruction, hunting pressure, and the same exotic pet trade that ushered them into the United States.

No one knows exactly how these pythons got out of their terrariums, and into the South Florida ecosystem, but the reigning theory is that a few founder snakes escaped or were released into Everglades National Park by owners surprised to find that the small hatchling they brought home grew up to eight feet in its first year. Out in the subtropical environs of South Florida, the pythons started breeding.

Native Range of the Burmese Python
Southeast Asia
Distribution of Invasive Pythons in Florida

The Florida Fish and Wildlife Conservation Commission and the Fish and Wildlife Foundation of Florida have now hosted two month-long Python Challenges to draw attention to the invasion these snakes are mounting in Florida, where they are eating their way through the native wildlife faster than even rabbits can reproduce. Their diet has so far included at least 40 species of prey, including animals as large as deer and alligators and two endangered species—the Key Largo woodrat (Neotoma floridana) and the wood stork (Mycteria americana). Researchers suspect that this list could grow, if it hasn’t already, to include endangered American crocodiles and Florida panthers.

Joining Sterrett in Florida were his teammates David Steen—a conservation ecologist at Auburn University and a de facto snake liaison on social media who regularly urges people to leave their backyard reptiles alone—and Sean Graham, a vertebrate biology professor at Sul Ross State University in Texas who occasionally goes by “Swamp Lion,” a nickname he shares with the cottonmouth snakes he studies. The fourth member of their team, Stephen Neslage—a television producer from Georgia—was no professional snake wrangler, but was game to try his hand at it.

Together, they spent five days trekking up and down dirt roads and poking at tussocks of grass as turkey vultures listed unsteadily overhead and airboats whined through nearby canals. But despite their expertise, none of these snake hunters saw more than this single unlucky python—which is not to say the didn’t walk by hundreds of these cryptic reptiles hiding in the vegetation, lurking in the shallow marshes, and blending into the background.

Despite their size, Burmese pythons are notoriously hard to find. Because of this, University of Florida professor Frank Mazzotti says no one really knows just how many of these hungry snakes have made a home in the canals and underbrush of South Florida. The most accurate estimates of Florida’s python population, he says, range from “a lot” to “too many.” Researchers guess that 10,000 snakes is likely the bottom end of that range, and since the year 2000, more than 2,000 Burmese pythons have been removed from Everglades National Park and surrounding areas.

Still, despite what looks like an intractable ecological challenge, scientists and wildlife officials all over the United States haven’t given up the fight, and are urgently studying these reptiles to try and figure out how far they might spread, and how to stop them.

An invisible invader

Mazzotti, a military history buff, compares battling the Burmese python invasion to fighting a war. And there have been stages of the conflict when its course might have changed. The first python in the Everglades was spotted in 1979. Then nothing until 1995, when two were captured one after another.

By the year 2000, a dozen pythons had been removed from the park, and park biologist Bill Loftus and curator Walter Meshaka wrote at the time that they considered the Burmese pythons to be established in the region. But without evidence of hatchlings or nests, not everyone was convinced.

Then, in 2002, a park ranger discovered four hatchlings—giving credence to the theory that the pythons being spotted in the Everglades weren’t just escaped pets. These snakes were established, and reproducing.

Yet despite these early indications that Burmese pythons were becoming permanent fixtures in South Florida, the source still hadn’t been cut off. A total of at least 99,000 pythons were imported into the U.S. between 1996 and 2006, with as many or more bred and traded domestically.

“Those were the days to respond,” Mazzotti says. He describes an invasion curve, where the area impacted grows as a product of time. At the lower end of the curve, acting quickly has the potential to eliminate invasive species with relatively little effort. At the top, significant resources go into keeping the populations of an already established invader from growing and spreading. But that’s where Burmese pythons are today, even though Florida banned people from buying them as pets in 2010, and the federal government put a stop to imports and interstate transport of Burmese pythons in 2012.

Michael Dorcas, a snake ecologist at Davidson College in North Carolina and a co-author of the book Invasive Pythons in the United States, suspects that Burmese pythons have multiplied so explosively in South Florida because they are filling a niche that has been empty of such large snakes for millions of years. Prey animals haven’t evolved defenses against these creatures that are lethal on land, water, and even in trees.

These cold-blooded reptiles are also able to survive in ecosystems as diverse as deserts, swamps, and montane forests at elevations up to 3,000 feet, because they’re particularly effective at temperature regulation. With the exception of an unusually cold Florida winter in 2009 that killed off at least 40 pythons, the snakes can survive chilly temperatures by retreating to burrows and slowing their activity, and females can keep clutches of eggs warm by contracting their muscles into shivering spasms. And these clutches of eggs tend to be pretty big. Depending on food availability, females generally lay between 40 and 50 eggs at a time, though sometimes can lay more than 100.

Hundreds of foot-long python hatchlings slithering out of a nest is a chilling thought for invasive species managers, considering the dramatic impacts these snakes have already had on native prey species. Dorcas and his colleagues reported massive declines in animals like raccoons, opossums, and bobcats in Florida that may be linked to a growing number of pythons.

Hunting for a game-changer

As of now, there isn’t a clear way to halt the python invasion. Again making the war comparison, Mazzotti says that what made the Allied Forces’ World War II campaign so effective is that it was two-pronged: while troops were fighting the ground war, scientists were also developing something that could end the conflict conclusively. Invasive species managers are actively seeking out and removing pythons, and they’ve even rallied troops in the form of amateur snake hunters competing in the Python Challenge, but they don’t have that anti-python atomic bomb. At least, not yet—but scientists are working on it.

The first step is developing a better way to find these incredibly cryptic creatures. One currently theoretical option is to use python pheromones to lure the many males that converge on one female during breeding season into a trap. But Mazzotti cautions that this just catches horny males—and the animals that propagate the species are the reproductive females. Others have been working with python-sniffing dogs, which are effective, but like humans, can’t access the wettest and most remote habitats of South Florida, and tire out in the heat. Infrared detectors that home in on the python’s heat signature have some potential, says Tylan Dean, the chief of the biological resources branch in Everglades National Park, but would tend to miss cold-blooded pythons that spend a lot of time in burrows, underground, or in water.

One approach currently being investigated involves following the genetic traces left behind by pythons in their environment—a process called eDNA testing that is not unlike the way cops link a criminal’s DNA to a crime scene. These traces can lead researchers to the places pythons colonize and the migration routes snakes use to get there. But, at least at the moment, this method only goes so far for eradication efforts, because while it can detect presence or absence of pythons, it can’t locate an individual.

“I don’t think we have a good grasp on which is the right tool for the job, or the next tool—the tool that we wish we had,” Dean says, noting that this is his personal opinion and that he is not speaking on behalf of the National Park Service. “When you bring the funding reality into the equation, it becomes pretty clear in my mind that there are not a lot of great opportunities.”

On the western edge of the Florida peninsula, biologist Ian Bartoszek with the Conservancy of Southwest Florida is equipping snakes with technology that can lead researchers right to their dens. These wired pythons are sometimes known as “Judas snakes,” but Bartoszek prefers to call them “snitch snakes… because they wear a wire and they rat on their friends.”

Working with Denison University, the Rookery Bay National Estuarine Research Reserve, and the USGS, Bartoszek and his team have captured 25 pythons, implanted them with tiny radio transmitters, and re-released them back into the mangrove swamps and upland wetlands of southwest Florida to track their movements and behavior. Bartoszek’s team regularly flies over these habitats, monitoring the snakes’ location so that researchers can find them later, on foot.

Last year, they tracked two of their radio-tagged males to a gopher tortoise burrow where they were tangled up in a giant mating ball with four other males and an egg-carrying female. “We reached back to the back of the burrow and felt a gopher tortoise that was trapped in there, and forced to watch all this sordid snake business,” Bartoszek says.

This year, using a combination of snitch snakes and a lot of active searching, Bartoszek’s crew caught more than 43 snakes over a three-month period, and many of these were egg-carrying females. Still, although he thinks he’s onto something, he’s not ready to wave the victory flag quite yet.

“I don’t know if we’ve made a dent, a dimple, or exactly what it is,” Bartoszek says but he can’t imagine that removing these hungry pythons from the wild is a bad thing for Florida’s native wildlife. “I don’t like putting that very impressive creature down,” he says, adding that he knows it’s not the fault of the Burmese pythons that they are in Florida, trying to survive. “But through the course of that animal’s life, there would have been a pile of native birds and mammals that it ate to get to that size.”

And what Bartoszek and his fellow snake scientists are learning about these creatures might help them manage the pythons in the future. Mazzotti, for one, is not about to give up the fight. He has hope for human creativity, he says. “Just because we don’t know what the solution to the problem is now, doesn’t mean we won’t know what the solution is five years from now.”

Rachel Becker

Rachel Becker is a freelance science journalist who writes about science, the environment, health, and technology. Her work appears in NOVA Next, National Geographic News and The Plate, Slate, Nature, Hakai, and others. Follow her on Twitter at @RA_Becks.

Kathryn Whitney

Kathryn Whitney is the former Photo Editor and Photographer for the California Academy of Sciences and bioGraphic, where she was able to combine her passions for science and photography every day. She is always ready for adventure, whether it’s outlasting a hailstorm while on assignment or galloping semi-wild horses across the Mongolian Steppe.

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