The preferred killing method is blunt force trauma, Frank Mazzotti, a wildlife ecology professor at the university, told The Washington Post on Monday. “Death is instantaneous, as is destruction of the brain. No pain is felt by the animal,” he said.

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That means, when available, the scientists use captive bolt guns that discharge a fast-moving metal rod, commonly utilized in the cattle industry and the weapon wielded by villain Anton Chigurh in the 2007 film “No Country for Old Men.”

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It also sometimes involves using deadly blows with other methods, like hitting them with hammers or swinging the iguanas hard into concrete. The scientists have gone out for six nights so far, often pulling iguanas right off trees as they sleep. Traps are set up in places like parks away from residential areas.

Mazzotti said the killing methods are in line with regulations established by various bodies, including the American Veterinary Medical Association.

The count so far: about 300 iguanas, some killed on the spot after they were trapped, with others later taken to be euthanized. The teams operate along a canal on the northeastern edge of the sprawling Everglades preserve in Davie, north of Miami.

Iguanas tend to colonize the man-made canals, the Florida Fish and Wildlife Conservation Commission says, an accidental proliferation aid for the lizards traversing the watery veins of Floridian suburbia. Density along water management areas makes iguanas more of a nuisance, requiring mass removals. Two nights alone netted about 200 iguanas.

The university’s work is underwritten by the commission. The commission provided $63,000 for the research project running through May that also includes weighing and measuring carcasses before they are properly disposed of at an authorized landfill, the Sun Sentinel reported.

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The iguanas, clearly, are not welcome. They do not even belong.

The natural habitat of the common green iguana stretches from Mexico through Central America and throughout the entire Amazon region in South America, including islands in the Caribbean and off the Brazilian coast, a map on the commission website shows.

According to the Sun Sentinel, iguanas arrived in Florida as pets, first appearing in Miami-Dade County in 1966, then in the Keys in 1995 before making a home of Broward County in 2001 and in Palm Beach in 2003. The total population is unknown, Mazzotti said, but the southern portion of the state has reeled from proliferating numbers. Iguanas can lay dozens of eggs at once.

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Iguanas are attracted to dense trees and fruit — kind of what Florida is known for. They destroy landscape vegetation, and their burrowing speeds erosion, leading to the collapse of sidewalks, foundations and canal banks, the commission says.

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If that is not enough, they can also transmit salmonella to humans that come into contact with water tainted by their feces — in swimming pools, for instance.

The commission carefully spells out how iguanas can be captured and killed. They recommend using nets, cage traps and noose poles for the famously agile, spiky-tailed creatures. But then it gets complicated.

You can kill one with a single blow from say, a shovel, but you must strike true. More than one blow could be animal cruelty punishable by prison time and up to $5,000, Ron Magill, an animal ambassador for Zoo Miami, told the Sun Sentinel.

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“Unless you have an animal that you can have in your hand, [killing humanely] is very hard to do,” Magill said.

Trapping and relocating iguanas to a more isolated place is also forbidden, Magill explained, because the practice could transmit viruses and bacteria to ill-equipped wildlife.

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Also: Do not poison or freeze them, experts warn.

Florida exotic pet veterinarian Susan Kelleher told the Sun Sentinel she considers the head-bashing inhumane and suggested sedating and euthanizing the iguanas. She did not return a request for comment. Mazzotti noted they do indeed euthanize iguanas.

Most residents can use pellet guns to kill iguanas, provided they are legal in their area. One resident, Gary Fishman, told the Sun Sentinel he has racked up more than 100 iguana kills with his pellet gun.

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“The iguana does not belong here,” he said. “They need to be annihilated. They can’t be relocated. So they must be destroyed.”

Mazzotti cautioned against that method.

The scientists have recovered iguanas with pellets lodged in their skin from botched kills, meaning the lizards, however loathed, probably suffered.

“That’s not humane,” he said.

Herman Wong contributed to this report.