Invading iguanas tear through Florida′s ecosystem | Environment | All topics from climate change to conservation | DW | 28.03.2018

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invasive species

Invading iguanas tear through Florida's ecosystem

Iguanas have arrived in the Sunshine State and are marching north, leaving a trail of destruction in their wake. Conservationists are hoping the human population might start to recognize these striking reptiles as food.

Florida's warm, sunny weather and extensive wetlands support a paradise of diverse flora and fauna. But when non-native species arrive and take advantage of the Sunshine State's enviable climate and rich biodiversity, they leave destruction in their wake.

Voracious predators like the Burmese python and Argentine black-and-white tegu lizard are the most famous culprits. But another, vegetarian, reptile is inflicting similar damage. Native to Central and South America and parts of the Caribbean, green iguanas have been spreading across South Florida after escaping or being released by pet owners.

"If they escape here in South Florida it's like Club Med – they're out there enjoying this wonderful environment, no pressures on them," zoologist Ron Magill told DW. 

Eating through ecosystems

Without any natural predators, iguanas are thriving in South Florida in particular. They can grow up to 6 feet (1.8 meters) in length, with appetites to match, and reproduce at an alarming rate. "One female can lay 30 to 40 eggs at a time," Magill says.

Sam Van Leer, founder of the Urban Paradise Guild

Sam Van Leer says iguanas are thwarting efforts to protect local flora

They munch through native plants and crops and crowd out smaller, native lizards. They also feed on flowering plants that butterflies depend on, and are blamed for wiping out the last known colonies of critically endangered Miami blue butterfly, which is found nowhere outside of South Florida.

Sam Van Leer is president of the Urban Paradise Guild, an organization dedicated to removing invasive plants in South Florida and restoring natural habitat through volunteer programs. Iguanas are a constant challenge to his replanting efforts.

"It is a common misconception, 'oh they look cool' and 'oh they don't really hurt anything,'" Van Leer told DW. "The reality is they are a plague that has been unleashed on our ecosystem. So when people see one, they see this neat-looking lizard, what they don't understand is the damage that they create."

Tearing up the canals

And they're not just tearing through Florida's wildlife. They're also causing serious infrastructure damage that could result in flooding in some areas.

Michael Kirkland is an invasive animal biologist in the South Florida Water Management District. "They burrow into the levees, if you get enough burrows, the levees will start to collapse in on themselves," he told DW.

Such attacks on infrastructure combined with the reptiles' impact on ecosystems can add up to billions of dollars' worth of damage, Kirkland says.

Along the canals that lead to Florida's Biscayne Bay, hundreds of iguanas can be seen sunning themselves on boats or scurrying along the sea walls.

Iguana auf einem Boot

There's little an iguana enjoys more than sunbathing by the water

"Iguanas love water," Magill said. "You'll often see iguanas on the banks of canals or on trees overhanging canals and any time they are threatened they will not hesitate to just jump in the water and they swim incredibly well. So the canal is like a freeway system to these animals."

It's a transit network that gives them access to all sorts of choice spots.

Uninvited exhibits

At the Zoo Miami, Magill, who works there as communications director, points out three iguanas idling in the cage of a 160-kilo gorilla. The moats around exhibits might keep the zoo's intended residents in, but they do nothing to keep the scaly invaders out.

The apes are used to living alongside the lizards, which are drawn to their food. But Magill says the parasites and diseases – including salmonella – they carry are a concern.

"We have a real risk there of cross-contaminating some of our exotic species at the zoo with whatever an iguana might be carrying," he says. As a result, the Zoo Miami is culling iguanas to keep their numbers down.

Fairchild Tropical Botanic Garden in Coral Gables has an iguana problem, too. Visitors, especially kids, love to see the striking reptiles. 

Ron Magill, Communications Director and zoologist at the Zoo Miami. Miami, Florida. Photo by Niall Macaulay.

Zoologist Ron Magill in his office at Zoo Miami, which has taken to culling iguanas to protect exhibits

"Sure they are cute. They look dramatic, so it can be a draw," director Carl E. Lewis admits. But the garden's extensive collections of rare tropical plants, including palms, cycads and flowering trees, are like a free buffet for the iguanas and hundreds have turned up to tuck in.

"Having giant vegetarian lizards running around – that is a big challenge for us," Lewis says.

Raining iguanas

Cold snaps are the only natural limitation on the iguana population here. To kill significant numbers, the temperature needs to be near freezing for at least four to five days. The last time this happened was in January, when a "bomb cyclone" brought unusually cold temperatures to the East Coast.

"We have this phenomenon in South Florida called 'raining iguanas,'" Magill says. "You come during a really cold day, in the morning, and iguanas will be falling out of trees."

The animals aren't actually dead, he explains.

"As the temperature goes down to 40 degrees, their body shuts down, they lose their grip and they fall out of the trees. They will turn a grey color, their eyes will sink in. It's a miracle that once they warm-up they will come back to life."

USA Kältestarre Iguanas in Florida

In cold weather, iguanas become paralysed and fall out of the trees

In 2010, plummeting temperatures nearly wiped out the iguanas at the botanic gardens. But some survived by burrowing under ground.

"Iguanas are at the edge of their ability to survive the winter. If we get a cold snap, they really get knocked back," Lewis says. "We just haven't had one for several years now, that's why our iguana populations are very high."

Conquering new territory

In fact, climate change could be a factor in the iguanas' spread. "There is an infestation that has been growing," Van Leer says. "Over the past five years, I would say it's getting significantly worse."

Magill says warmer weather in recent years has enabled them to move north. He predicts it'll take about another five years for them to reach Orlando, some 380 kilometers north of Miami.

The Florida Fish and Wildlife Conservation Commission offers workshops on the dos and don'ts of shooing iguanas for homeowners wanting to drive them out of their gardens.

But Magill thinks Florida residents might need more of an incentive to really go on the offensive. 

"In places that they're found naturally, in tropical Central America, for example in Panama, they have farms for them because they eat them – they're a delicacy," Magill says.

"I am somewhat hoping but that trend might take place here in South Florida soon. If people understand that they are a delicacy, we can control their numbers."

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