MIAMI — So much for all the efforts to slow the proliferation of Burmese pythons in the Florida Everglades over the last two decades, including with paid contractors, trained volunteers and an annual hunt that has drawn participants from as far as Latvia: The giant snakes have been making their way north, reaching West Palm Beach and Fort Myers and threatening ever-larger stretches of the ecosystem.
That was one of the few definitive conclusions in a comprehensive review of python science published last month by the U.S. Geological Survey, which underscored the difficulty of containing the giant snakes since they were first documented as an established population in the state in 2000.
Little is known about how long Burmese pythons live in the wild in Florida, how often they reproduce and especially how large the state’s python population has grown, according to the review, which called the state’s python problem “one of the most intractable invasive-species management issues across the globe.”
Nor is it known how exactly they travel. The review theorized that South Florida’s extensive network of canals and levees “may facilitate long-distance movement by pythons,” though it suggested that slithering and swimming to points north may take awhile.
“One python transited continuously for 58.5 hours and traveled 2.43 kilometers in a single day,” the review said of a snake followed with radio tracking.
More research should be conducted to develop and evaluate new tools to eradicate pythons and to refine existing ones, the study found, adding that controlling the species’ spread is critical to protecting the Everglades. Earlier studies found that Burmese pythons, which are nonnative apex predators originally from South Asia, had decimated native species, including wading birds, marsh rabbits and white-tailed deer.
Pythons found in Florida have measured longer than 15 feet and weighed more than 200 pounds, the review found; even hatchlings can be more than two feet long.
The pythons’ voracious spread is all the more alarming given the billions of dollars that the state and the federal government have spent on restoring the Everglades, the review noted, calling invasive species “one of the greatest threats to restoration success.”
Florida, with its subtropical climate, numerous entry ports and prolific live animal trade, has at least 139 established invasive species, meaning that they are reproducing in the wild, according to the state Fish and Wildlife Conservation Commission. More than 500 nonnative species have been reported in the state over time.
Pythons, like invasive iguanas, have been known to emerge from the occasional South Florida toilet bowl; the review notes that while Burmese pythons have mostly been spotted in and around Everglades National Park and other swamplands, many have also been found in Naples and the western outskirts of Miami.
Once a year, the Fish and Wildlife Conservation Commission holds a python hunt open to the public, challenging people to find and remove as many snakes as they can. Participants must take a training course online or in person about humanely killing pythons using either preferred mechanical methods, like a stun gun, or manual ones, like hunting knives, since the hunt does not allow the use of firearms. Last year’s winner took home $10,000 for hunting down 28 pythons.
Dustin Crum, who has been hunting pythons for a decade, took home $1,500 for capturing the longest snake in the competition, an 11-footer. He won in the same category in 2021 after catching a 15-footer.
“We started out doing this stuff as a hobby and just couldn’t believe we could catch giant constrictors like that in the wild,” said Mr. Crum, 42, who now hunts pythons full time. The state pays hunters $50 per foot for the first four feet of snake and $25 for each subsequent foot, he said, as well as an hourly rate. Outside of the state-sponsored competition for the public, Mr. Crum does use guns to kill the snakes.
“I’ll say a little prayer: ‘Hey, it’s not your fault,’” he said.
Sometimes, scientists ask to get the pythons alive so that they can be tracked. Hunters like Mr. Crum deposit them in designated drop boxes during night hunts and email researchers to come get them in the morning.
Pythons became popular exotic pets in the United States in the 1970s. Some eventually grew so large that their owners released them into the wild. By 2000, scientists had documented multiple generations of pythons living across a relatively large geographic area in the Everglades and Florida’s southern tip.
The realization that pythons were prodigiously reproducing and nearly wiping out native species helped lead to regulations restricting python importation and ownership. But by then, it was too late to stop their spread.
Detecting pythons, which like to hide in marshes and thrive in remote habitats, is so challenging that experts do not know how many exist in Florida, though they estimate that there are at least tens of thousands. More than 18,000 have been removed since 2000, including 2,500 in 2022, according to the Fish and Wildlife Conservation Commission.
Melissa Miller of the Institute of Food and Agricultural Sciences at the University of Florida is helping lead a large-scale python removal project that also hopes to get a better sense of the snakes’ abundance by putting trackers on more of them and measuring the reproductive output of more females. (She is also part of a team of experts at the university, known as the “Croc Docs,” that researches wildlife in South Florida and the Caribbean.) Another part of the project will use drones to track many tagged pythons at once. Someday, a genetic biocontrol tool might emerge to help suppress the population, she said.
“We don’t really have a reliable estimate of how many are out there,” Dr. Miller said. “They’re kind of a cautionary tale to not to release pets, to make sure you report invasive species immediately.”
Florida makes it easy with a hotline: 888-IVE-GOT1.
Pythons are so large that they are not easily kept in enclosures to study them. The U.S.G.S. review suggested building a research center to conduct captive and small-scale trials.
In late 2021, a team from the Conservancy of Southwest Florida found likely the largest Burmese python ever recorded in the state: a 215-pound female with 122 eggs inside her.
“It helps you visualize what it ate, in pounds of native wildlife, to get to that,” said Ian Bartoszek, the environmental science project manager for the group.
If there is any good news in the U.S.G.S. review, it is that there have been no reports of humans in Florida being killed by wild pythons, which squeeze their prey to death before swallowing it; captive pythons are responsible for the few recorded fatalities.
Python breeding season generally extends from November to March or April, Mr. Bartoszek said. The team at the Conservancy of Southwest Florida uses tagged male pythons as “scouts” to lead researchers to females. This season, a V.I.P. — “that’s Very Important Python,” Mr. Bartoszek said — named Jesse led the team to two large females within two weeks.
“We’ve had to do a lot of kayaking out to some of them this season,” he said. Female pythons in the area that the group studies have been smaller lately, he added, a sign that tracking and hunting them might be making a dent in the number that survive long enough to get big: “It’s getting very hard for those animals to find us females,” he said.
Hurricane Ian, the powerful Category 4 storm that crashed into Southwest Florida last September, did not have much effect on the pythons his team tracks, he added. Prolonged cold snaps have killed off some snakes in the past, the U.S.G.S. review noted, but such weather has become increasingly rare in southern Florida.
Mr. Bartoszek said pythons had adapted over time to Florida, with those closer to the coast behaving slightly differently than those inland. But native species have adapted, too, and python hatchlings now have a few predators: snakes, alligators and at least one bobcat that was caught on camera preying on a clutch of python eggs.
“The Everglades,” Mr. Bartoszek said, “is fighting back.”
Susan C. Beachy contributed research.