FLORIDA CITY, Fla. — Deer flies swarmed around Frank Mazzotti and Joy Vinci as they stooped to get a closer look at the creature thrashing around in a metal trap they had laid off a weedy dirt road. Inside it was what some biologists consider the most troublesome invasive species in the Everglades: not a Burmese python, but a 24-inch lizard, the Argentine black and white tegu.

It thumped its long tail like a snare drum — a tactic the species uses to shift predators’ attention to that expendable appendage (it can grow a new one). Ms. Vinci, a wildlife biologist, was not fooled. Wiping her brow in the 91-degree Florida heat, she attached a cloth bag to the end of the cage and then carefully opened it, shooing the tegu inside.

As she knotted the bag, the animal went limp, playing dead. That didn’t work either: The tegu, along with three others trapped earlier, would be taking a one-way trip out of the marsh, in Miami-Dade County, and to the University of Florida’s Fort Lauderdale Research and Education Center.