Pythons are invading Florida. Meet the scientists fighting back.

Betrayal, sex pheromones, and a lot of snake wrestling.

A male python in an ambush posture. Brian J. Smith

The Burmese python mating season can be a cramped affair. In southwestern Florida, the snakes sometimes gather in burrows dug by gopher tortoises. For python-tracking scientists, this presents an opportunity. In 2015, Ian Bartoszek was searching for pythons amongst the scrub when he got a ping from one of his radio-tagged snakes, dubbed Kirkland. He and his team quickly located the burrow this snake had sought out—and realized that Kirkland was not alone. Another tagged male was in the hole, along with four other males and a 14-foot female.

“There were 240 pounds of python in one hole in the ground,” says Bartoszek, a wildlife biologist at the Conservancy of Southwest Florida in Naples. “They just kept coming out, one after the other, and it just didn’t stop.”

The scientists gathered their scaly bounty, and rescued a gopher tortoise they discovered trapped at the back of the burrow. “He was forced to watch all of this snake behavior,” Bartoszek says.

While the snake bonanza made for an intense extraction day, it was not the only time Kirkland has been extracted from a girlfriend’s scaly embrace. The team is nabbing every female and stray male they can find on their patrols, and they’re not the only ones. Every year, hundreds of pythons are dragged from the South Florida wilderness and roads. Scientists worry that that is nowhere near enough.

They’re stepping up the fight against the invasive snakes that have been plaguing Florida for more than 15 years. Their weapons include “Judas snakes” like Kirkland that lead the way to their fellow pythons, sex pheromones, and volunteer python patrols. Year by year, they’re learning more about the snakes and how to find them. They aren’t likely to vanquish the Burmese python, but they might yet knock the population down to manageable levels.

Masters of disguise

There have been reports of pythons in Everglades National Park since the 1980s. The first pythons were likely escaped pets; a few pythons may have fled a breeding facility that was destroyed during Hurricane Andrew. In 2000, scientists realized that there was an established python population in the Everglades. Since then, the snakes have swept across southern Florida. A few stray pythons have been spied as far north as Jacksonville and the Florida Panhandle.

Scientists aren’t sure how much the snakes could spread; they may be capable of living as far north as the Gulf Coast or coastal Southeast. “We went from finding just a couple a year up to hundreds a year being removed and spread over a pretty large area, so they’re marching forward pretty quickly,” says John Willson, an ecologist at the University of Arkansas in Fayetteville.

python hiding in grass
Pythons are difficult to spot with the naked eye. John Willson and his colleagues once released 10 pythons into a 100 square foot cage. Then 19 people, many of them experienced herpetologists, were each given half an hour to search for the snakes among the grass, bushes, and water. Between them, the volunteers managed only two python sightings. “For every one we see, we’re probably missing many. We just don’t know how many right now,” Willson says. Brian J. Smith

Pythons grow fast and can reach lengths of more than 17 feet. A single female can lay up to 87 eggs in the wild. “These snakes grow to very dangerous sizes and have voracious appetites—they’ll basically eat whatever fits in their mouth and if it doesn’t fit exactly they’ll still try,” says Rocky Parker, a reproductive physiologist at James Madison University in Harrisonburg, Virginia. “They’re almost built to be invaders.”

Yet these giant snakes are almost invisible to people. Often, they will not break cover even if you walk on top of them. “A 15-foot-long, 150 pound python can absolutely vanish in a little patch of grass,” Willson says. “It really severely limits our ability to even assess their populations, let alone control them.” More than 2,000 pythons have been removed from Everglades National Park and the surrounding areas since 2002. However, scientists have no reliable estimate for how many lurk in the park’s remote wilderness.

The main technique that volunteers and scientists use to spot pythons is simple. On warm, humid summer nights, people drive up and down the roads, hoping to find a python crossing the street. During the winter, the snakes are less active, but can sometimes be found basking in the sun along canals and levees. There are also state-sponsored snake hunts that draw people from around the country.

These efforts are likely doing little to quash the python population. “If we are dealing with in fact tens or hundreds of thousands of pythons, then removing 500 is not solving anybody’s problem,” says Brian Smith, a scientist for Cherokee Nation Technologies, a contractor for the United States Geological Survey. A handful of females can easily lay enough eggs to replace all the pythons removed by snake wranglers in a year.

To really control pythons, we must make them easier to find. So Auburn University researchers are calling in detector dogs. Meanwhile, Smith is using eDNA—genetic material shed in specimens like skin and poop—to detect whether pythons have colonized an area. When the snakes have not yet been seen, the DNA fragments could sound an early warning.

python crossing the road
A python crosses the road in Everglades National Park. Brian J. Smith

Smith would also like to learn more about when and where the snakes are most active. Being able to predict when pythons will be on the move would give snake wranglers an edge.

There’s a chance that pythons are drawn to roads or waterways, or congregate on high ground during the breeding season. “If 99 percent of the landscape is inaccessible and that’s where all the population is, we are nowhere near being able to control that,” Smith says. “On the other hand, if they come to us at some time of year, there’s hope that what people are doing right now is working.”

Smith says he’d like to be wrong about how many snakes are packed into the Everglades and how densely they have colonized the landscape. But, he says, “When you go out and you’re walking in the marsh and you can’t find one that has a tag in it…and you’re standing on it, it’s hard to think that they’re not everywhere.”

Scaled betrayal

Scientists have another, more devious trick up their sleeves. During the breeding season, pythons become very sociable. Females are followed and courted by posses of lusty males; Smith and his crew have found groups of up to eight pythons intertwined. In recent years, they have begun to implant radio transmitters in a handful of males and follow them to their trysts.

During the breeding season, which spans December to April, the researchers fly over the Everglades in a small plane to pick up radiolocations for these Judas snakes. Then they trek in to see if the males have found a partner. The flat, grassy terrain is deceptive; it once took Smith eight hours to hike two miles off the road to pick up a python and return. “Every single step, your foot sinks into the muck a little bit, and so it’s just like a suction cup,” he says. “You’re fighting through sawgrass and you’re just beaten and bruised by the time you get back.” When a snake is too remote to be reached on foot, they call in a helicopter.

Yet this labor-intensive approach to python gathering is worth it, Smith says. He and his team have calculated that catching snakes with the Judas technique costs about $30,000 per year. This is more expensive than searching for pythons by hitting the roads on a regular basis. However, the Judas technique yielded pythons during the winter months, when no snakes were out on the roads. “Not only are we catching animals at the time of the year with the Judas technique when road cruising doesn’t work, but we’re catching much larger animals,” Smith says. “We’re really getting at the reproductively mature animals in the population.”

Bartoszek is also a master of the Judas technique, although he prefers to think of his snakes as sentinels that help him thwart the species’ spread. “They’re kind of defending a certain line for us, they’re kind of standing guard,” he says.

Bartoszek and his colleagues track about 20 radio-tagged pythons year-round, and stalk them most intensely during the breeding season. “Usually we’re rewarded with a pretty big python that that animal was after,” Bartoszek says. They nab the female and any hopeful nearby males and follow the sentinels to their next partner.

female snake laying eggs
A female python and eggs Ian Bartoszek and his colleagues removed. “We’re not going to get them all; we’re not deluding ourselves here,” he says. “We’re just trying to hold the line with our sentinel animals and keep this from becoming a bigger problem.” Leif Johnson, Conservancy of Southwest Florida

To date they’ve removed hundreds of breeding adult pythons—that together added up to about 4 tons—from a 20 square mile area of southwest Florida near Naples. Their largest catch was 185 pounds.

Each sentinel male has a number and name, “So we know them a little more personally,” Bartoszek. One of his VIPs (very important pythons) is Johnny, who led them to 13 pythons this season. Another heavy hitter is Jaeger, who gave up three breeding females. “A male Burmese python is the best female python detector on the planet,” he says.

Wrangling the snakes can be a chaotic venture. “When you see them, they generally see you and they’re calculating their escape plan, so you have a few seconds usually before that animal’s going to bolt,” Bartoszek says.

They try to grab the animal behind its neck and wrestle it down—preferably out of water. Last year, the notorious Kirkland had just one lady-friend. “Damn if he didn’t decide to hook up with her in the middle of a cattail marsh that was waist-deep,” Bartoszek says. It took three people to hold onto the female while he pulled himself onto a floating matt of ferns and walked down her back. “If you don’t get that neck right away, you’re in for a rodeo,” he says.

Once the snake is subdued, they put it in a bag so one of the team’s wildlife technicians can hoist it onto his back and carry it back out. They then bring the snakes to the lab to be humanely euthanized. “We have a lot of respect for these animals, they’re definitely beautiful creatures and we don’t like having to put them down, but we know the toll that they’re taking on the environment,” Bartoszek says. “I’ve seen small pythons regurgitate deer and alligators and everything in between.”

By focusing on a small area, the team hopes to make a dent in the snakes’ numbers. “We’ve infiltrated the local population—we know our neighborhoods, we know the specific males, their home ranges,” Bartoszek says. “We’re watching them go further and further away to find mates. That tells me we’re gaining ground.”

The smell of sex

Each spring in Manitoba, Canada, garter snakes gather en masse to look for partners and form giant mating balls, in which dozens of males surround a single lucky female. Pheromones prompt the snakes to ball up, says Parker, who studies how reptiles use sexual odors to find mates. When he saw videos of pythons gathering in similar clumps, he realized that chemical signals must be important for bringing these large snakes together, too.

He’s working to extract pheromones from shed python skins with funding from the Florida Fish and Wildlife Conservation Commission. He and his colleagues are hoping that pheromones might be used as bait, and are building a library of different chemicals to figure out which ones lure males. Over the next few years, they will figure out which of the 30 to 50 chemicals most interest the snakes and test how they prompt the males to alter their behavior.

a glass flask full of liquid
Compounds extricated from Burmese python shed skins. Michael Avery and his colleagues have found that males can tell the difference between male and female extracts. JMU Photography

To remove the pheromones, the skins are left to soak overnight in a chemical called hexane. This pulls out the pheromones but leaves the rest of the skin behind intact. Once the hexane evaporates, a yellowish waxy coating remains in the flask. To the human nose, the pheromones have an almost floral note. “You might say it smells sort of like a sweet crayon,” Parker says.

Meanwhile, Parker’s teammate Michael Avery has been building simple mazes to put the pythons through their paces at the U.S. Department of Agriculture’s National Wildlife Research Center in Gainesville, Florida. He and his colleagues encourage female pythons to slither through the Y-shaped maze, then bring in males and film their pursuit. They’re studying how males change their behavior when they’re on an actual female’s trail, and whether female pheromones can elicit the same response.

This is not a high-speed chase. Male pythons sometimes pause for hours in the maze. “They are very hesitant, they don’t act impulsively…like garter snakes do,” Parker says. “Garter snakes get on a sex pheromone trail and they just go.”

In perusing the videos, Parker’s team has noticed that a male python’s behavior actually gets more elaborate when he senses a female. He will raise his head off the ground, and sometimes backtrack and return later. “They also do these cute little head shakes, where the python just moves his head slightly from side to side,” Parker says. This routine might be an attempt to make sure they have zeroed in on the female’s trail.

python in a maze
A male python follows a female scent trail through a maze. Michael Avery, USDA NWRC

A female python secretes pheromones along the ground where she slithers. Eventually, scientists might dupe males by sprinkling these chemicals in trails leading to traps. In the past, traps baited with food haven’t been very effective—these snakes are ambush predators, and prefer to wait for their dinner to come to them. But using pheromones to trick the snakes into believing a female is nearby might make traps more successful during the breeding season, Parker hopes.

Pheromones may also turn Judas snakes into even better double agents. Parker has partnered with United States Geological Survey scientists Bryan Falk and Bob Reed to make radio-tagged males more obvious to their peers. He’s already experimented with implanting crystalline estrogen into male garter snakes, which prompted the snakes to release chemicals that made them smell like females. “They’re super attractive to all these other animals in the field,” Parker says. “They start courting them like they’re females.” He repeated the experiment with brown tree snakes and saw similar success. So implanting estrogen into male pythons might draw out their well-hidden fellows.

High stakes

Burmese pythons are far from the only invasive species afflicting Florida. One worrying newcomer is the Argentine black and white tegu. These four-foot-long lizards are friendly pets—and ruthless predators with a powerful sex drive. They tolerate cold weather well, meaning they could potentially spread into other states.

Wild hogs, responsible for destroying fields and crops across the state, aren’t Florida natives either. Nor are fire ants and lionfish. And the state spends $100 million each year just on combating invasive plants. But Burmese pythons are especially unnerving, Smith says. “The idea that this giant snake that doesn’t belong here is here just really is in people’s hearts and minds.”

And the pythons are causing major problems. Willson and his colleagues have been tracking the python’s impact on mammal populations. In the pythons’ stronghold in Everglades National Park, the situation is dire. “Most of the mammals have disappeared, and this is everything from rabbits all the way up to declines in things like bobcats and white tailed deer,” Willson says.

This spring, the team reported that fewer freshwater turtle eggs are being nabbed by raccoons and other mammals that pythons prey on. This might be good news for the turtles, but it concerns Willson. “They may be changing all sorts of aspects of the South Florida ecosystem, not just the species that they prey upon,” he says.

shed python skin
A shed Burmese python skin. JMU Photography

The pythons have begun to infiltrate the Florida Keys, home to endangered species like the Key Largo woodrat. And in recent years, mosquitoes have started feasting more on rats as pythons have gobbled up larger mammals. The rats carry diseases that the mosquitoes can pass on to people. So controlling pythons will be a matter of public health.

“It’s tempting to be very pessimistic about the situation,” Willson says. “I still have hope that we will find at least ways to control them in small areas.”

The best chance of wiping out any invasive species is to eradicate all the trespassers early on. It’s decades too late for this tactic to work in southern Florida. “Are we ever going to get rid of the Burmese python? Probably not,” Bartoszek says. “It’s probably a permanent part of our Everglades ecosystem.”

But we can fight back by honing our ability to detect and capture pythons, add new weapons like the Judas technique and pheromones to our arsenal, and prevent pythons from getting a foothold in fragile habitats like the Florida Keys. “We have to live with pythons now,” Smith says. “But the more we understand them, the better chance we have of protecting the ecosystem we have left.”