When researchers with the Conservancy of Southwest Florida announced they’d bagged the heaviest Burmese python ever captured in Florida earlier this summer, the catch highlighted a secret weapon in the effort to control the invasive snakes: amorous male snakes.
A male python named Dion led the team to the 215-pound female, then went on to find four more female snakes this past breeding season.
“If there's a bunch of haystacks out there and we're looking for these needles in the haystacks,” said wildlife biologist Ian Bartoszek, who runs the Conservancy’s python research program, “the males are the magnets.”
The males can follow the scent of a female python’s sex pheromones during the mating season. The Conservancy, which implanted its first radio tracker in another male snake named Elvis in 2013, now has 40 male scout snakes outfitted with trackers. So far, the snake posse has helped bag about 26,000 pounds of pythons, Bartoszek said.
“So 13 tons of python, with a few people and constant pressure over time by following our male scout snakes,” he said.
Researchers also made another surprising find during a necropsy: the female held 122 unfertilized eggs. Previous estimates on clutch sizes maxed out at about 100.
Using pythons to track other pythons has been around since at least 2005 when the University of Florida captured and inserted radio trackers in 17 pythons. The method had previously been used to hunt down brown tree snakes in Guam, wherea massive invasion that swept the island led to power outages and wiped out most of the native birds in Guam’s forests. The U.S. Geological Survey and National Park Service have since been working on expanding research into how sex pheromones can be used to entice pythons into following each other or even into traps.
What researchers like about the method is its range. Hunters participating in the state-managed hunt run by the Florida Fish and Wildlife Conservation Commission that ended Aug. 14, mostly find pythons on roads and levees. But radio trackers implanted in scout snakes can lead researchers to pythons deep in wilderness areas. That’s where the snakes can do more damage, gobbling up deer, bobcats and other animals that native wildlife, including the endangered Florida panther, need to survive.
“The majority of the time, we're hacking and slashing through the woods,” Bartoszek said.
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Since the first python was discovered in Everglades National Park in 1979, they have exploded across the landscape, becoming the invasive poster species for a state overrun with damaging nonnative plants and animals. Like other exotic animals, researchers suspect pet owners started dumping them when they became too large — a well-fed python can grow up to 9 feet in just a year. Between 1979 and 2009, USGS estimates 300,000 pythons were imported to the U.S. Hurricane Andrew may have also played a part when the storm hit a breeding facility for exotic reptiles.
In 2006, the first nest with mating snakes was discovered, confirming conservationists' worst fears: the pythons had begun breeding and increasing numbers on their own. In a cost analysis that included crunching the dollars spent to save endangered species that pythons can eat, including wood storks, Key Largo wood rats and American crocodiles, a 2007 study found a single python could cause up to $6 million a year in damage.
“Once they get to a certain size, they are the apex predator,” said Frank Ridgley, a wildlife veterinarian and director of conservation and research at Zoo Miami. Ridgley has surgically implanted dozens of trackers in pythons for the park service and USGS. “This is the mouth that eats everything in the Everglades.”
The Conservancy tracked the large female in the Picayune Strand, a patchwork forest of cypress and pine that is underwater for most of the rainy season. The forest stretches across more than 100 square miles and can only be accessed off-road by foot, bike or horse.
“It’s mostly impossible to navigate,” Bartoszek said.
Which is where the scouts can come into play.Past research has shown that given a choice, pythons will follow other pythons, regardless of sex.
“There can be a little bit of preference during breeding season, but they do like to just follow each other,” Ridgley.
The snakes use their forked tongue to taste the air, where they can pick up traces of pheromones. Each fork transmits signals to an organ in the roof of its mouth.
“So it's like listening,” Ridgley said. “If they have a chemical scent on one side stronger than on this side, they know to go that direction.”
How close pythons have to be to pick up each other’s scent is not known, he said. UF research found that the snakes tend to have a home range, with at least one captured snake slithering nearly 50 miles to return home. Females tend to stick to that home territory, the research found, but males may roam for miles looking for amorous females during the breeding season.
Once they find each other, it’s party time.
Pythons can form mating balls, like other snakes, with multiple males wrapping themselves around a single female.
“That's where the scout snakes come in. They really play a role there,” Ridgley said. “Because that's when the females are laying off the pheromones, saying, hey, okay, I've been ignoring you guys all year, now's the time. And then many males can find a female at the same time.”
The female snake’s eggs can then be fertilized by different males.
That’s why capturing the reproductive females can have an exponential effect, researchers say.
A few weeks after the Conservancy announced its capture, state python hunters in the Big Cypress National Preserve found a nest with a female, 23 unhatched eggs and 18 hatchlings. They returned the next night to find another breeding python nearby that was more than 17 feet long.
The breeding season usually begins in December and runs through April, Ridgley said.
Eventually, Bartoszek thinks the Conservancy’s scout snake effort can be scaled up to other parts of South Florida. But to do that, he said researchers need a landscape-wide population study with a valid estimate for the number of wild snakes.
“Is it 70,000? Is it 7000,” he said. “We don't need to get it down to the individual, just a target so that can get us closer to the mark and we can know if over time the efforts are working.”
Past estimates put the number at 100,000, but the number can change depending on conditions and even the time of year, he said. That work is now underway.
Even with an estimate, Bartoszek says it’s unlikely Florida will ever be python-free.
“If we keep pushing back at these females, maybe we're catching up in some corners, but it's very much the hydra effect,” he said. “Once you get your handle on one, things are popping up somewhere else.”
