Florida’s invasive iguana population is booming. And that’s a problem.

The state has no plan for how to deal with it.
A green iguana strolls around Eco Golf Club in Hollywood, Florida on Oct. 28.
A green iguana strolls around Eco Golf Club in Hollywood, Florida on Oct. 28. [ MATIAS J. OCNER | Miami Herald ]
Published Nov. 26, 2019

The green iguana is the most in-your-face invasive species in South Florida.

Unlike the infamous but elusive Burmese python, iguanas freely mingle with people — and often act like they own the place. One jaunty male was videoed recently strolling Miami Beach’s Lincoln Road while others pose unperturbed for pictures along the crowded promenade. They sun on docks and decks across South Florida, poop in pools and graze on gardens. They’ve undermined the kitchen at a golf course restaurant in Cooper City and canal banks along Miami’s Little River.

They’ve now been spotted in the wild across much of the state, everywhere from Gainesville down to Key West, where they have a habit of shorting out power lines.

Florida wildlife managers know they’re a problem. Citizen complaints about the invasive reptiles had become so numerous that they made a tentative stab at doing something about it early this year, giving the green light for residents to “humanely kill green iguanas on their own property whenever possible.”

But the state quickly softened that approach after backlash from animal rights groups, to the point where the agency now refuses to even explain how to humanely dispatch one.

Still, there is no getting around the fact that South Florida has an exploding population of giant exotic lizards and no real plan to do anything about it. The sparse research on their numbers, how fast the population is growing or how much damage they are doing is narrowly focused or outdated.

In 2007, a group of scientists including researchers from the University of Florida and state agencies sought to document the geographic distribution, reproduction and potential ecological impacts of the green iguana. They tallied up 3,169 documented lizard sightings from May 1992 through December 2006 from just south of Lake Okeechobee to Key West. While nobody’s counting them today, it’s fair to guess that there are easily that many on Key Biscayne alone.

As for impacts, based just on anecdotes, it’s a lot. One agency, the South Florida Water Management District, has dealt with so many issues from big burrowing lizards that it’s working on what appears to be the state’s first formal assessment of iguana damage — if only to drainage canals crisscrossing much of the region.

The only thing wildlife managers and scientists can say for sure is that the iguana population has come back with a vengeance from a freeze that killed off many of them a decade ago. Iguanas are vulnerable to cold — their body temperatures depend on conditions outside — and enter a lethargic state when temperatures dip below 50 degrees, sometimes dropping from trees in chilled stupor.

They eventually die if a serious cold snap sticks around for more than three days. But that hardly ever happens in South Florida and with climate change raising average temperatures, extended cold snaps may occur even less frequently.

“They are in paradise,” said Frank Mazzotti, a University of Florida wildlife biologist and reptile expert. “Their populations are growing and their range is also expanding.”

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Second-class invasive species

Florida’s relationship with iguanas is complicated and often contradictory. People kind of like them, but don’t really want them on their properties. Even many people who want them removed from their homes don’t like the thought of killing them like rats or roaches.

“A lot of people have mixed feelings about iguanas because they are cool animals: they look exotic with their beautiful colors and aren’t dangerous,” said Brian Wood, a trapper who’s been catching iguanas in South Florida for more than 10 years. “People have a hard time treating them as the pests they really are.”

Brian Wood holds an iguana he caught near The Danians Condo in Dania Beach, Florida on Oct. 28.
Brian Wood holds an iguana he caught near The Danians Condo in Dania Beach, Florida on Oct. 28. [ MATIAS J. OCNER | Miami Herald ]

They’re not aggressive and don’t hurt pets, though their droppings can be a source of salmonella bacteria, which causes food poisoning. And unlike the Burmese python, another invader that poses a well-documented threat to the Everglades and has wiped out entire populations of small mammals in the threatened ecosystem, the mostly vegetarian iguana is only a problem to a select number of native critters, owing to its appetite for certain plants and bird eggs.

That all makes the iguana a sort of second-class invasive species, which perhaps helps explain why not much funding or research have been directed to study or control the big lizards.

Green iguanas were first found in Miami-Dade in the mid 1960s in Hialeah, Coral Gables and Key Biscayne, and were later spotted in Collier, Lee, Monroe, Palm Beach and Broward counties around the late 1990s. Like the Burmese python, they were probably kept as pets and escaped or were simply released when they got too large. Since the 1980s, the green iguana has been hugely popular in the pet reptile trade as it’s perceived as a low-maintenance exotic animal.

“You can give them salad, you don’t need to worry about feeding them live prey as is the case with the Nile monitor lizards or snakes,” said Todd Campbell, a biology professor at the University of Tampa whose research focuses on invasive species. Florida’s sub-tropical climate and abundant vegetation creates confidence among iguana owners that they can release their pet lizards in the wild and they will go on living happily, said Campbell, who worked on a 2016 Department of Agriculture-led study of a long invasive reptiles, including green iguana.

In that assessment, the lizard ranked 15th out of 37 problematic invasive reptiles and was designated a “high management concern.” But the study also classified it as having a narrow potential range and suggested that no research on control methods was needed. Another species, the less commonly seen black spiny-tailed iguana, was actually considered a bigger threat, included among the seven “highest impact concern” reptile invaders alongside the Argentine giant tegu, the Nile monitor lizard and the Burmese python.

Today, the most up-to-date information on Florida’s green iguanas comes from field observations, sightings by the public and researchers reported on a multi-agency website managed by the University of Georgia.

The green iguana tops the list of commonly spotted reptile invaders, with nearly 7,000 reports. The map of sightings outlines a population range concentrated along the Atlantic Coast in Broward, Martin, Miami-Dade, Monroe and Palm Beach Counties and along the Gulf Coast in Collier and Lee Counties. There have also been reports as far north as Alachua County, according to the Florida Fish and Wildlife Conservation Commission. The native range of green iguanas extends from Central America to the tropical parts of South America and includes some Caribbean islands.

With the lush landscaping and warm climate of South Florida, these plant-eating reptiles can multiply incredibly fast and scientists say they also have used South Florida’s extensive network of canals to spread and move around as they please, munching on plants, with orchids and hibiscus apparent favorites.

Females are ready to reproduce at around two years of age. They dig egg chambers that may contain as many as 80 feet of interconnected tunnels and multiple entrances, and lay anywhere from 14 to 76 eggs. Green iguanas can live up to 10 years in the wild, according to the Florida Fish and Wildlife Conservation Commission, and there are no real predators to keep them in check.

A pet becomes a pest

Along with reports from homeowners whose gardens have been invaded, stories of iguanas causing damage to infrastructure also are increasingly common.

The South Florida Water Management District is spending more money and time dealing with iguana damage. The Little River canal, or C-7, in northeast Miami-Dade, is overrun with the exotic reptiles. They build complex and extensive burrow systems that can become deeper when females are nesting, undermining docks, seawalls and canal banks.

They’ve been digging so many holes on the Little River Canal banks that washouts are frequent, forcing maintenance crews to rebuild the banks and do constant stabilization work around the 35 square miles that make up the C-7 basin.

A large male Iguana basks in the sun along with a female at the Miami Beach Golf Club on Oct. 3. Mature male iguanas turn orange to attract females.
A large male Iguana basks in the sun along with a female at the Miami Beach Golf Club on Oct. 3. Mature male iguanas turn orange to attract females. [ JOSE A. IGLESIAS | Miami Herald ]

The district has hired trappers to remove iguanas in the past, only to have the lizards return in greater numbers a few weeks later, said spokesman Randy Smith. The situation reached such a critical point that water managers now want to quantify the damage to their facilities.

Until encouraging people to humanely kill them, state wildlife managers have taken only selective aggressive steps to control green iguanas. Several years, ago, in the Florida Keys, iguanas were gobbling up the host plant for the endangered Miami blue butterfly. The Florida Fish and Wildlife Conservation Commission hired a trapper who removed hundreds of iguanas from Bahia Honda State Park to protect a butterfly barely hanging onto existence.

“Though we can’t eradicate them, we do focus our control efforts where we know they pose an immediate threat to other native species and ecosystems,” said Eric Sutton, executive director of the Florida Fish and Wildlife Conservation Commission.

Other indirect impacts to wildlife have been reported recently: iguanas have disturbed beach nesting birds like the Least Tern, and have eaten the eggs of these birds, the Florida Fish and Wildlife Conservation Commission said. They also compete for space with vulnerable native species, such as burrowing owls and gopher tortoises.

Even ZooMiami had to find a way to deal with its iguana problem. The lizards were digging into the moats, annoying the gorillas, giraffes and spider monkeys in the Africa section. Once, two fierce iguana males were fighting over territory and blood was shed. Visitors were distressed.

The last straw was when Frank Ridgley, a wildlife veterinarian and the zoo’s head of conservation and research, saw an iguana on a water fountain.

“At that moment it became a health hazard,” he said. Iguanas caught at the zoo are euthanized.

Quick destruction of the brain

But not everyone has lethal injections handy to painlessly dispatch a pest iguana.

The Florida Fish and Wildlife Conservation Commission’s recommendation to kill them “whenever possible” on private properties, issued on July 3, didn’t spell out exactly how to do it. The commission said iguanas also can also be killed on 22 public lands in South Florida without a permit but they are protected by state anti-cruelty laws so only “ legal methods” are allowed. Poison is forbidden but other than that, the agency gave no specific guidance on how to get rid of them.

Animal rights advocates quickly accused the Florida Fish and Wildlife Conservation Commission of inciting cruelty and took the agency to task for not taking a more pro-active approach in managing the non-native species.

“Randomly killing these wonderful animals is not only cruel but also foolish, as it won’t curb their numbers in any significant way and will lead only to untold suffering at the hands of laypersons unqualified to ensure a humane death,” the People for the Ethical Treatment of Animals said in a letter to the Florida Fish and Wildlife Conservation Commission in July. PETA said that humanely killing an iguana “requires immediate destruction of the brain in order to avoid prolonged survival and suffering for as long as one hour,” according to the letter.

The Humane Society also said that Florida had failed to properly regulate the pet trade, the primary cause of the rise in populations of invasive amphibian and reptile species in the state. “Attempting to reduce iguana populations without addressing the root causes of the problem will only result in a continuous cycle of killing, with no end in sight and no genuine relief from conflicts residents are experiencing,” wrote Kitty Block, CEO of Humane Society US.

A few weeks later, the Florida Fish and Wildlife Conservation Commission tempered its advice, but still didn’t spell out how people should kill iguanas humanely.

“Unfortunately, the message has been conveyed that we are asking the public to just go out there and shoot them up. This is not what we are about; this is not the ‘wild west.’,” Commissioner Rodney Barreto said at the time.

When the Miami Herald asked for a Florida Fish and Wildlife Conservation Commission expert to demonstrate or explain humane killing methods, the agency would only point to the internet or suggest calling an experienced trapper.

“There are numerous sources of information on the internet regarding specific methods to trap and remove iguanas,” Kipp Frohlich, director of habitat and species conservation at Florida Fish and Wildlife Conservation Commission, said in emailed responses to questions. “If a person is not comfortable or capable of safely removing iguanas from their property, the best course of action is to seek assistance from professional wildlife trappers.”

That’s what Dawn Braeseke decided to do after iguanas dug holes under the kitchen of her golf course’s restaurant earlier this year, leading to a $40,000 plumbing repair job to fix dangling pipes and foundation damage. She hired a pest-control service that specializes in the pesky lizards.

“They busted through the foundation and caused the pipes to collapse,” said Braeseke, who runs Cooper Colony Country Club in Cooper City. At least 20 juveniles and two large males lined a small area near the course’s entrance one late morning in October. They scurried away and hid under the deck of a neighboring house as a trapper approached.

“Total elimination isn’t the goal because it’s just not possible,” said Blake Wilkins, co-owner of Hollywood-based Redline Iguana Removal. “The idea is to make things manageable.”