An Argentine black and white tegu is caught in one of 160-plus traps set out by a University of Florida research team. The group collaborates with the Florida Fish and Wildlife Conservation Commission, the National Park Service, the U.S. Geological Survey, the U.S. Fish and Wildlife Service, and the South Florida Water Management District to contain and reduce the tegu population Photo: Karine Aigner

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Invasive Reptiles Are Taking Over Florida—and Devouring Its Birds Along the Way

Birds like Roseate Spoonbills and Burrowing Owls are ending up in the stomachs of hungry pythons and Nile monitors. Is it too late to stop them?

It’s a sweaty morning last June on the outskirts of Tampa, and droves of reptile enthusiasts are streaming into an air-conditioned expo center. Some have woken early to trek out to the Florida State Fairgrounds to get first crack at the animals of Repticon, a weekend-long extravaganza that’s similar to a baseball card convention, except instead of mint-condition Mickey Mantles and Pete Roses there are green anacondas and meat-eating lizards. One vendor’s table is covered in flimsy plastic catering trays that are filled with ball pythons. Others are selling Asian water monitors, gargoyle geckos, yellow rat snakes, and bearded dragons. A guy strolls by wearing a “Snakes Lives Matter” t-shirt. Another man, who has a three-foot-long lizard slung across his chest like a bandolier, is at a nearby booth admiring a young boa constrictor that’s twirling around his girlfriend’s fingers. Price? $100. Sold.

Roughly 60 Repticons take place each year, from Phoenix to Oklahoma City to Baltimore, attracting an estimated 200,000 visitors. These shows represent but a tiny sliver of the live-reptile trade, a loosely regulated industry that spans the globe and generates an estimated $1.2 billion in revenue annually, according to the United States Association of Reptile Keepers. In much of the continental United States, these cold-blooded creatures aren’t likely to fare well outdoors should they escape or be set free. But the sub-tropics of South Florida are different, and the best adapted have not only survived in the wild, they have thrived. To date the Florida Fish and Wildlife Conservation Commission, or FWC, has identified 50 types of non-native lizards, turtles, crocodilians, and snakes within state limits, more than anywhere else in the world.

For the birds of Florida, this blitz of exotic predators poses an existential-scale threat. The Burmese pythons, which stalk wading birds in the Everglades, have become so menacing that the state has hosted derby-style competitions to catch them. Farther north, Nile monitors—the largest lizard in Africa—have been terrorizing a population of Burrowing Owls in the city of Cape Coral. And on the outskirts of Florida City, just outside Everglades National Park, egg-eating Argentine tegus could soon raid the nesting grounds of one of the last remaining populations of the endangered Cape Sable Seaside Sparrow. Each of these reptiles found their way to Florida via the pet trade—but while most people acknowledge that’s a leaky pipeline, few agree on whether and how to plug it.

Take Ed Poelsma, who’s wandering Repticon with Pugsly, a five-and-a-half-foot-long black-throated monitor that’s a close relative of the Komodo dragon. Pugsly is a stunning creature that looks to be from prehistoric times, with claws like steak knives, camouflaged skin, and a muscular tail. What does Pugsly eat? “Meat,” Poelsma says. “He would eat anything you put in his cage that’s meat. Literally anything.” No, Pugsly has never bitten Poelsma, and yes, he considers the giant lizard to be part of his family. He takes Pugsly for walks in his neighborhood, maintains an Instagram page for the animal, and happily answers questions from curious onlookers. You don’t need a permit to buy a Pugsly of your own, and that’s how Poelsma thinks it should be. “If you want to look at invasive animals in the wild, the very worst thing in the world is a domestic cat,” he tells me. “Go to the local ASPCA or local pound and look at all the dogs and cats . . . But everybody wants to blame the reptile owners for being an irresponsible pet owner.”

It’s a sentiment that almost everyone I meet at Repticon echoes, including Greg Graziani, who has starred on National Geographic’s The Python Hunters and now runs a reptile-breeding facility and serves as an amnesty point for FWC. If someone wants to get rid of a reptile they shouldn’t have or can no longer control, Graziani can arrange a no-questions-asked drop off. Of course invasive reptiles are a problem, he says, but so are invasive plants, trees, and mammals. And as for the risks Argentine tegus, Burmese pythons, and Nile monitors pose to the menagerie of birds that depend on Florida’s lush landscapes, Graziani is empathetic but unconvinced. “The bird people are worried,” he says. “I understand their concern. But I haven’t seen the science.”

Truth is, scientists have never seen anything quite like this.

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t's the Monday morning after Repticon and I’m in a vacant lot in Cape Coral watching Bob Mondgock smack a package of frozen chicken with the claw end of a hammer. He pries free a hunk of raw poultry and tosses it to the back of a spring-plated trap in hopes of luring in one of the invasive Nile monitors that haunt this Gulf Coast city.

Over the years Mondgock has tangled with more monitors than he can remember. He works for the Cape Coral Environmental Resources Division, a six-person unit that might very well have been the inspiration for Parks and Recreation. Mondgock is the Ron Swanson of the group: a mustachioed Libertarian who will under no circumstances let me turn on my tape recorder. Before getting back into the truck, he clips an armful of fronds from a nearby bush and piles it around the trap. It’s less about camouflage than it is about making sure there’s enough shade to keep curious cats and raccoons from baking to death if they get stuck.

Nile monitors have no business in this hemisphere. As their name implies, they should be basking along the shores of Africa’s Nile Delta, but they got popular in the pet trade and rumor has it that the owner of a now defunct pet store, scheming a source of free inventory, let some loose behind his shop so they would breed in the wild. Unsurprisingly, the lizards quickly fanned out across Cape Coral’s extensive canal system. The first sighting likely dates back to before 1990, though it wasn’t until the early 2000s that they began regularly popping up in people’s backyards. If you’re not accustomed to large lizards, an adult Nile monitor dashing across your lawn might be terrifying. They can top seven feet, swim like Michael Phelps, and eat rodents, birds, rabbits, wasp nests, venomous rattlesnakes, poisonous cane toads, and, according to some residents, cats and dogs.

There’s no telling how many Nile monitors are out here. Since 2000, the city has logged more than 2,500 sightings and trapped 564 of the animals. Over all those years, though, no one has uncovered a monitor nest, an unsettling tidbit given that the lizards can lay up to 60 eggs at a time. Conservative estimates put their population at 1,000, a lowball number in Mondgock’s eyes. The city usually sets traps in response to residents calling in sightings, he explains, and many residents are so accustomed to the animals that they don’t bother calling one in. Today Mondgock will bait 11 traps, all within view of nice homes with pools, screened-in porches, and garages.

A captured Argentine black and white tegu. Video: Karine Aigner

As we drive from site to site, we pass a handful of dusty lots where Burrowing Owls perch on wooden stakes and look like adorable stuffed animals. That the city is home to one of the world’s largest populations of Burrowing Owls is a point of pride among some residents, not to mention a good tourism draw. The owls are staring down a long list of threats, including significant habitat loss, and FWC declared them a threatened species in November 2016.

It's known that Nile monitors eat Burrowing Owls—after all, the lizards are expert burrowers and ground hunters. What’s unknown is the number of owls they have devoured. One of the first confirmed cases dates to May 2005, when a woman saw a large monitor in her yard with one of the tiny tawny owls clenched in its jaws. Unfazed, she grabbed a flowerpot and threw it at the lizard. It dropped the owl and bolted away, but the bird did not survive. At least two other instances of monitors eating owls have been reported, and it seems certain that other attacks have gone unseen and undocumented.

Owls aren’t the only birds in monitors’ crosshairs. The lizards hunt cooperatively and are known to team up to lure birds off their nests so they can pillage the eggs, according to a report by Todd Campbell, a biologist at the University of Tampa and a leading expert on Nile monitors. “Many of Florida’s wading birds would be an easy target while foraging in mangroves and along tidal creeks and artificial canals,” the 2008 report warns, “and Nile monitors are excellent tree-climbers, so the nests of wading birds are also at risk.”

Back at Repticon, I saw at least five different types of monitors for sale. It’s a family of lizards that has roughly 70 species and only two—the Komodo dragon and the Nile monitor—are now tightly regulated here. FWC classifies the Nile monitor as a Conditional Species, along with only seven other reptiles, including the Burmese python and reticulated python (at nearly 30 feet, one of the largest snakes in the world). These species can’t be sold as pets, but with the right permits you can have them for commercial, research, and exhibition purposes. Dozens of other monitor species—crocodile monitors, Argus monitors, tree monitors—can be brought and sold no problem.

It’s a situation that draws criticism from both sides. Those who would like to see more control over the reptile trade consider it a gaping regulatory hole that could allow new invasive species to flourish. Those in the pet trade see it as evidence of how arbitrary and inconsistent the rules are. When I met Ed Poelsma and Pugsly at Repticon we were standing a few feet away from a female Asian water monitor that had a $1,000 price tag. Under the right conditions, it could grow up to 8 feet long, weigh 100 pounds, live for 15 years, and is every bit as capable of surviving in a South Florida suburb as a Nile monitor. The two animals have similar diets, reproductive habits, and hunting tactics. “A Nile monitor is basically the African version of an Asian water monitor,” Poelsma told me, pointing at the one for sale. Yet one is regulated and one is not.

Mondgock, the city employee, isn’t keen on discussing whether or how the pet trade should be controlled other than saying that Nile monitors “ARE. NOT. PETS.” He’s been bitten, scratched, peed on, and pooped on enough times (he was chasing them, not the other way around, he says) to know that these animals never play nice.

Two days after we part ways, one of the 11 traps we set nabs a three-foot Nile monitor that was first spotted climbing a resident’s front door. Like nearly all the monitors Mondgock traps, it was placed into a sealed plastic tube and exposed to a lethal dose of chloroform. Death by asphyxiation—a grisly fate, but what other options are there?

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iological invasions aren't necessarily blitzkriegs. It doesn’t matter if a pet store releases a few dozen lizards or a hurricane damages a breeding facility and sets free hundreds of snakes, as has happened. Some of the invaders die off, scooped up by predators or unable to adjust to their new environs. Others find food, find a mate, and survive. It’s in those early days of their arrival, before generations of the species are hatched, that there’s a chance at eradication. But with each new egg that’s fertilized and each animal that reaches sexual maturity, the monetary and ecological costs of the problem goes up. Biologists call this the invasion curve, and right now Nile monitors fall somewhere in the middle. Any hope of eradication in Florida faded long ago, but it may be possible to keep them contained to a few small pockets around the state—one is in Cape Coral, another is in Palm Beach County, where President Trump’s Mar-a-Lago resort is located.

Keep following the invasion curve upward, past the point of containment, past the Nile monitor, all the way to the top, and you will find the Burmese python. This apex predator can grow more than 18 feet long and was for a long time one of the most popular snakes in the pet trade. Now, there are estimated tens or hundreds of thousands of Burmese pythons in South Florida and they’re eating everything—rabbits, rats, bobcats, deer, even alligators. On the invasion curve, they fall in the “resource protection and long-term management” section. In other words, they’re taking over, and our only hope is to safeguard what they have not yet destroyed.

“Pythons are definitely eating birds,” says Brian Smith, a biologist who works for Cherokee Nation Technologies, a company contracted by the United States Geological Survey to help manage the invasive Burmese python population. A few years ago, Smith went to capture a python in Everglades National Park. The snake was in a shallow marsh and Smith noticed a bulge in its stomach. He moved in and grabbed the python near the base of its head. Suddenly two bird feet popped out of the snake’s mouth. A moment later, another two feet shot out. The snake writhed and in one fell swoop regurgitated a pair of full-grown Great Blue Herons. Smith couldn’t believe his eyes as the corpses poured out and flopped to the ground. Both birds’ heads were missing; other than that the animals were intact and easy to identify.

Smith’s gruesome anecdote raises an important question: Could Burmese pythons devour resident birds of the Everglades the same way they did the small mammals? In 2012, a team of researchers reported in the Proceedings of the National Academy of Sciences that marsh rabbits, raccoons, and opossums had all but vanished from sight in Everglades National Park. One of the culprits, they suggested, was the arrival of the Burmese python, which records show was established in the park around 2000. If that’s the case, it took the snakes just a decade to eat their way through that section of the ecological menu. Knowing whether they have completely shifted their diet to wading birds for their next course is difficult to determine, though.

“I think that it is possible,” says Christina Romagosa, an assistant research professor at the University of Florida, “but I am having a hard time showing it because we really don’t know what’s out there for them to eat.” Some evidence sits on Romagosa’s desk: several plastic bags containing the remains of a Roseate Spoonbill. One is filled with bones; another has the bird’s feet. The biggest bag holds dozens of soft pink feathers, some still in sheath. A few days earlier, the remains of the spoonbill were found in the gut of a Burmese python that had been run over by a motorist. “It looks like maybe this bird was molting,” Romagosa speculates.

As a graduate student, Romagosa began amassing one of the largest running known data sets of wildlife imports and exports, which she used to show that buying, selling, and transporting exotic animals around the world is one of the root causes of the invasive species epidemic. Her current work, however, isn’t as neat and tidy as building databases of import-export records and involves analyzing a fair amount of snake poop. Teams at Everglades National Park and The Conservancy of Southwest Florida collect dead Burmese pythons, perform a necropsy, and freeze whatever fecal matter happens to be inside. Then Romagosa’s technicians—Eric Suarez and Diego Juarez-Sanchez—perform the odoriferous task of washing the waste in a sieve and analyzing the remains to determine the snake’s last meals.

It is anyone’s guess as to what one heap of python poop might reveal. There can be tufts of mammal fur, fragments of bird feathers, crushed bones, disembodied beaks, and occasionally flecks of eggshell, and accurately identifying what species trace evidence originated from is tedious. Sometimes the bird parts are so degraded that Romagosa cannot identify the species, so she ships them off to Carla Dove, head of the Smithsonian Institution’s Feather Identification Laboratory. Dove is very concerned by the variety of birds eaten by pythons. “It’s crazy,” she tells me. “These birds didn’t evolve with this kind of predator.”

To date, at least 39 different bird species have been found in python remains. They include the federally threatened Wood Stork; Magnificent Frigatebird; Great Blue Heron; Little Blue Heron; Red-whiskered Bulbul; Snowy Egret; and Pied-billed Grebe. Rails and White Ibis are common finds, and entire Limpkin and guinea fowl eggs have been removed from the belly of these beasts. Despite the dozens of bird species extracted from python stomachs, not to mention documented sightings of a python in a Wood Stork nesting colony, Romagosa doesn’t know that the snakes are developing a taste for birds, just that they’re eating them. Maybe pythons are selecting certain prey or maybe they’re snacking on whatever is nearby. “We get a lot of ibis in the diet, but that’s just maybe because there are a lot of ibis out there,” she says.

The Roseate Spoonbill is the newest species to be added to the pythons’ hit list, and it is setting off alarm bells among some scientists. “It’s a really bad thing,” says Jerry Lorenz, director of research at Audubon Florida’s Everglades Science Center. Spoonbills, he explains, are a key indicator species for measuring the success of Everglades restoration efforts. Fewer nesting spoonbills could mean inadequate habitat—or a voracious predator. “From a statistical perspective, that is a variable that should be entered into any model; but if you can’t quantify it, you can’t control for it,” Lorenz says. “The question becomes: How many spoonbills are being eaten by pythons? And of course that’s an impossible question to answer.”

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ile monitors and Burmese pythons are similar in that they came, they destroyed, and they got regulated. They are cautionary tales, but legislators have been slow to heed the warnings. Case in point: the Argentine tegu, a squat lizard with a taste for eggs that isn’t hard to find on the outskirts of Miami. To get a glimpse of these beasts I’m in the back seat of a White Ford F-150, sitting next to a large plastic container labeled “Dangerous Reptiles.” At the wheel is Brittany Mason and riding shotgun is Sarah Cooke, both of whom are trapping Argentine tegus on behalf of the University of Florida’s Croc Docs lab. The truck lurches along dirt service roads in southern Miami-Dade County, stopping every few minutes so the women can check one of the 150 different traps that are nestled in the bushes.          

Tegus are bizarre-looking lizards with enormous jaw muscles that resemble jowls. They are omnivorous eating machines that have in the past decade rocketed up the invasion curve and are now so ubiquitous in this stretch of Florida that some grad students refer to it as Tegulandia. There are even tales of a local fast food joint that became renowned for tegus that burrowed under the drive-thru box and scared the hell out of unsuspecting customers.

In their native South America, tegus have a fondness for eggs. They raid caiman nests and eat tinamou, a ground-dwelling bird. But as I’m learning today, they seem equally enticed by store-bought chicken eggs. An hour into the trip, Cooke walks down a pile of rocks holding the first trapped tegu of the day, a juvenile that’s 16 inches long, give or take. She shakes the lizard into a canvas bag, tags it with a pink piece of tape, and tosses it into the Dangerous Reptiles bin. About an hour later, the team bags the second tegu of the day, and then the third, which is taken on the grounds of a firing range. They secure the fourth only after Mason throws the truck in park, jumps out of the driver seat, and, like a reptile-fighting ninja, kicks the trap closed. Minutes later, they trap tegus five and six only a few hundred yards from a busy highway. With ruthless efficiency, the young women clear and re-bait the entire trap line and haul out a bin full tegus.

Just like Burmese pythons and Nile monitors, tegus got a toehold in South Florida through the pet trade, where they are beloved as docile, intelligent, and affectionate companions. The fight against them is now at an inflection point. “We’re out of the eradication part of the invasion curve and we’re heading up through containment,” says professor Frank Mazzotti, who leads the Croc Docs lab. “The question is: Are our efforts going to be enough?”   

It’s a loaded question with dramatic implications. The lizards have already raided alligator and turtle nests in Florida, and the area where we bagged six is mere miles from one of the last populations of the Cape Sable Seaside Sparrow, a federally endangered species that builds its nest inches off the ground. Since 2014, Mazzotti’s team has trapped 1,418 tegus. The good news is that the gut contents of a few hundred tegus that were trapped, killed, and necropsied didn’t have any sparrows or sparrow eggs. The bad news is that there could be thousands of tegus out there—a female lays about 30 eggs per clutch—and they appear to be slowly making their way north, south to the Florida Keys, and west toward the edges of Everglades National Park. There are additional populations on the Gulf coast, farther north in Tampa, and near Orlando.

A mapping tool called EDDMapS tracks observations of invasive species, including black and white tegus. You can view individual reports by zooming in on the map above and clicking the pins. Interact with maps of other reptiles and submit your own sightings at the EDDMapS website

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Making matter worse is that tegus slip into a hibernation-like state for several of the coldest months each year and are better equipped to handle cooler temperatures than the Burmese python. Given their hardiness, these animals could potentially establish themselves far beyond South Florida and have already been spotted across the panhandle.

Yet for all the trouble they are causing and all the risks they pose, tegu sales aren’t regulated in Florida. Unlike the Nile monitor and Burmese python, FWC does not classify tegus as a Conditional Species. Head to a Repticon, drive to a pet shop, or jump on Google and you can buy one for a few hundred bucks. It seems counterintuitive that federal and state resources are being allocated to trap and kill tegus, while at the same time there is minimal oversight of the trade. I asked FWC if tegus should be listed as a Conditional Species and what steps the agency is taking, if any, to limit the trade. In response, an agency spokesperson wrote that they are “considering many approaches to minimizing the impact this species may have in Florida” and that the agency is “putting resources towards assessing the risk of species and making any further changes if warranted.”

I posed the same question to Phil Goss, president of the U.S. Association of Reptile Keepers, a trade organization that advocates on behalf of reptile owners and breeders. “FWC has been talking about doing something for four or five years and nothing has come to fruition,” he says. “There’s so much red tape.” But given what we know about tegus’ ability to survive cooler temperatures and the fact that there are several established populations, should a pet store in Florida be able to sell one to anyone who walks in? Goss pauses, then laughs: “It’s really hard to answer that question,” he says. “You hate to see responsible people punished because of the actions of irresponsible people.”

For Mazzotti, there is no question that the tegu trade should be more tightly regulated, and the fact that it’s not is indicative of a much bigger problem. When it comes to exotic species, whether it’s a fish a snake or a plant, the United States has a wait-and-see mentality in which the species first needs to become established and damage the environment before anything is done. “Once you can see the impact that a species is having,” he says, “it’s too late.”

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any of the people at Repticon agree with Mazzotti's assessment that it’s often too little too late when it comes to invasive species. “There are so many different invasive species here in Florida that it’s a crapshoot,” says Scott Galusha, who is cradling his pet tegu, named Zero, as we speak.

Galusha is quick to concede that the bad actors in the pet trade are responsible for the pythons, monitors, and tegus, but insists the industry has cleaned up its act in recent times. The best way to stop the introduction of new invasive species isn’t more regulations, he says, it’s educating pet owners and making sure buyers know what they’re getting themselves into when they decide to take on a giant lizard or snake. As for the future of tegus, Galusha doesn’t expect the state to crack down on them anytime soon. “We have never had to worry about licensing or chipping [tegus],” he says. “I don’t see it happening. If it does they are going to have to grandfather quite of a few of them in because so many people have these guys as pets.”

Scientists, state regulators, and land managers are already stretched thin in the battle against invasive reptiles, and the challenges are only growing. A recent federal court ruling rolled back enforcement of the Lacey Act, which for nearly three decades has largely prevented the importation of brown tree snakes, yellow anacondas, and other “injurious wildlife” species. Now anyone can transport them across state lines, leaving FWC scrambling to find a stopgap while simultaneously dealing with the dozens of destructive reptiles already in play.

In the absence of a regulatory fix, scientists have turned to more creative solutions for fighting reptiles in the wild. Romagosa has worked with dogs trained to sniff out pythons, and others are using a tool called environmental DNA, or eDNA—which analyzes water samples for genetic material left behind by animals—to look for the presence of pythons in bird rookeries. Last year Mazzotti even teamed up with FWC to bring two Irula tribesmen, who are world-renowned for their snake-tracking skills, to Florida from India. Over a couple of months, they snatched nearly 30 pythons, including a 16-foot-long female, an impressive haul when compared with locals’ efforts.

All of these undertakings are aimed at bolstering early detection and rapid response, which Mazzotti says is key to staying one step ahead. To that end, one of the most helpful tactics could be as simple as having birders report invasive species they come across while out in the field. Florida has set up a toll-free hotline to call in sightings—1-888-IVEGOT1—and the University of Georgia’s Center for Invasive Species and Ecosystem Health has developed smartphone apps that allow users to report potential sightings and upload pictures of the animal in question. It’s the old “see something say something” approach, and it helps biologists respond faster to invasions and better target their trapping efforts.

Before leaving Florida I stop at Audubon's Corkscrew Swamp Sanctuary, where I am greeted by a symphony of woodpeckers and croaking amphibians. It’s a welcomed respite, a swampy enclave seemingly free of invasive pythons, monitors, and tegus—at least for now.

“We see them as a serious threat,” says Shawn Clem, research manager for the Audubon Florida Western Everglades Research Center, located in Corkscrew. Rather than wait for the worst and then act, Clem and her team are busy sharpening their front-line defenses. Recently they have increased their efforts to survey mammal populations; a drop in the numbers could be an indicator that pythons are near. She also formed a rapid response team with Mazzotti’s lab, and most of Corkscrew’s back-country staff are now trained to safely capture and remove pythons.

Clem knows that Corkscrew will not remain impervious to these invasive species forever. In recent years a handful of live tegus and dead pythons have been found along the nearby roads, just a few miles outside the sanctuary. She is worried about what these exotic predators might mean for Wood Stork, turkeys, bobwhite quail, and all the other species of birds that call Corkscrew home. “We are being vigilant,” she says. “We’re ready.”

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