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Alien Iguanas Overrun Florida Island

Maryann Mott
for National Geographic News
May 24, 2006
 
Boca Grande, Florida, bills itself as the Tarpon Fishing Capital of the World. But the tiny island town in the Gulf of Mexico is fast becoming known for something not touted in tour guides.

Up to 12,000 non-native black spinytail iguanas—many 2 to 3 feet (60 to 90 centimeters) long—have infiltrated the resort community. (See a map of southeastern Florida.)

The reptiles ruin landscaping, spark power outages, and weaken protective sand dunes with their burrows.

Some residents have even found the creatures floating in toilets.

"For years the iguanas have had the run of the island," islander Beverly Furtado said.

"Everybody thought they were cute in the beginning and didn't mind them being around."

But attitudes have now changed.

Lee County commissioners recently approved a special tax on Boca Grande residents to cover the cost of removing the invasive species.

"It's a major problem," said commissioner Bob Janes, who pushed for the levy.

"We're trying to nip it in the bud."

Iguana Baby Boom

Last week a five-person Boca Grande county advisory board met for the first time to draw up a plan to eradicate the reptiles.

By July the panel must submit their plan's budget, which will determine the size of the "iguana tax" Boca Grande residents must pay.

According to Janes, the community has only recently become concerned about the iguanas. He says that in 1997 residents believed the invasive species was harmless and turned down an offer from the county to get rid of the iguanas.

Since then the population has exploded.

The reptiles have no natural predators on the 7-mile (11-kilometer) Gasparilla Island, where Boca Grande is located. (Browse a guide to South Florida reptiles.)

In the past five years the iguana population has reportedly jumped from 2,000 to 12,000.

Biologist Jerry Jackson, of Florida Gulf Coast University in Fort Myers, says a female iguana can lay up to 80 eggs at a time and may do so two or three times during breeding season.

"These animals in their homeland [Mexico] have predators, parasites, and diseases that they didn't bring with them. So their populations here can get out of control," said Jackson, who was hired by Lee County to study the iguana problem.

The biologist says the lizards, which can swim, may have already dispersed to nearby islands. He adds that, if the reptiles reach the mainland, it will be almost impossible to stop their spread.

Bad Pets

It's believed the iguanas were introduced to Boca Grande in the 1970s, when a resident brought a few lizards back from Mexico as pets and later released them.

Jackson says that, unlike green iguanas, which can be tamed, black spinytail iguanas "don't make good pets."

The reptiles use their thorny tails like whips. And once their mouths, which bristle with sharp teeth, clamp down on something, they don't let go.

The sheer number of iguanas on Gasparilla Island—about ten per human resident—is causing a multitude of problems for people and wildlife.

Jackson says the reptiles' feces may carry salmonella bacteria, which can cause food poisoning, typhoid fever, and other ailments. The iguanas also devour sea turtle eggs and shorebird nestlings.

In addition, the lizards dig large burrows, which undermine sand dunes on the island. The dunes help protect people and property from storm surges.

Iguana Vigilantes?

John Bourgoin, who serves on the Lee County iguana advisory board, says he'd like to see a volunteer workforce trap and kill the reptiles.

"We want to take the matter into our own hands," he said, adding that doing so would relieve residents from paying an additional tax.

Bourgoin says money left over from a street-lighting project could pay for the 60 or so traps needed.

"Since the beginning of the year just three of us have gotten rid of about 235 [iguanas]," Bourgoin said.

"So, we're on the right track, I believe."

Jackson, the university biologist, says a much broader effort is needed, including closing off nesting burrows and controlling Brazilian pepper, a non-native shrub with a bright red fruit that is a mainstay of the iguana's winter diet.

"What we've done in the past year is to look at the annual cycle of the animals, and we've been trying to figure out weak points in their natural history," Jackson said.

He said that, by attacking the iguanas in the winter when they're stressed and "getting rid of exotic plants that they are feeding on at that time, we could exercise a natural control on them, to some extent."

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