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The black spiny tailed iguana invasion unsettled islanders as the slippery beasts disrupted gopher turtle habitats and gorged on the eggs of the endangered hard shells while growing exponentially in numbers. They also chomped through hibiscus and other leaves, seeds and berries. They seemed to be everywhere overrunning the island just three years ago.

Now, after trappers have shot and killed thousands of iguanas, the initial surge seems to have been blunted, Dr. Michael Avery of Wildlife Research told about 30 people at a Friday seminar at the Boca Grande Community Center.

Avery said trappers have also been highly successful in fighting back by poisoning larger iguanas of reproducing years, which stunts the growth of the population as a whole.

After collecting data for two years, Avery said the average body mass and size of the iguanas found in Lee and Charlotte counties is in decline. That means there are fewer males and females of reproductive years to add to the population.

"Reproductive potential is down 48 percent," Avery said. "More than 60 percent of the iguans are now juveniles too small to lay versus 25 percent in 2008."

Boca Grande will never be able to wipe out its iguana population, Avery said. It's unclear just how many are still here.

"We really don't know," Avery said. "They can lay 80 eggs in a clutch."

The only true iguana predator is man although foxes, bull snakes and hawks have been known to snack on them, too.

"I wish ospreys would eat them but ospreys are lazy fishermen," said Mike Kennedy, a Charlotte County trapper.

After a 5-0 vote to renew the Boca Grande iguana control contract with the USDA, Chairman Ron Gutman of the Municipal Services Benefit Unit Advisory Committee said he thought it was $104,000 well spent. The recommendation will be sent to the Lee County Commissioners.

Trapper George Cera protested the contract going to a government agency instead of the private sector. He also questioned how safe zinc phosphide is for the family pet and other possible secondary victims.

"There's nothing good about zinc phosphide," Cera said.

A zinc phosphide pill stuffed in a marschino cherry has proven to be an irresistable canape for the iguana, which later dies of a chemical reaction to the drug.

"These animals do regurgitate the pills but they still die," Avery said.

Avery said trappers were careful not to use a poison that could kill other unspuspecting animals such as the family pet. The bait is also used in a controlled setting.

"We're not going to just lay it on the ground," Avery said.

When the iguana gulps the tasty cherries with a toxic center, they are poisoned by a chemical reaction when their body converts the zinc phosphide to a toxic gas, Avery said.

Zinc phosphide also has the added benefit of risking no true secondary poisoning, except possibly in dogs and cats, he said. Most predators and scavengers that feed on rodents are unaffected because the zinc phosphide does not accumulate in the rodent's muscles or other tissues since it turns to gas form before it kills.

"Presenting the bait in a way that exposes the lizards to it and not anything else is really critically important," Avery said.

Nationally, there have been a few poisonings of domestic livestock, dogs and cats through accidental exposures usually.

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