NORTH KEY LARGO -- Jim Duquesnel walks into the hardwood hammock just off County Road 905 in the Crocodile Lake National Wildlife Refuge and peers into a wooden snake trap.
Next, the U.S. Geological Survey biologist continues up and down three rows containing some 24 traps in all. He looks inside each one. They're empty too.
If Duquesnel were a hunter, he'd surely be disappointed. But for a scientist, and indeed for Key Largo in general, this empty harvest is good news because it suggests there still aren't many Burmese python making the trek from the Florida mainland onto the island.
But that doesn't mean Duquesnel isn't worried.
"The population on the mainland is making more and more pythons every year," he said. "The frequency of them making it here it is going to increase."
Duquesnel's work on the python traps is one of the tasks he shares with fellow biologist Michelle McEachern. Together, they're the USGS's front line as the agency attempts to stop pythons, tegu lizards and other invasive species that are increasingly common in South Dade from making it to the Florida Keys.
It's a crucial task. In Everglades National Park Burmese pythons are wiping out a range of small mammals, such as marsh rabbits and opossums, a National Academy of Sciences study released this year found.
Meanwhile, the tegu lizard, a black and white Argentine import that typically grows to around three feet and reaches a weight of eight pounds, is a forager that thrives on eggs that are laid on the ground. If they arrive here it could mean problems for a range of Upper Keys species, including box turtles, burrowing owls, nighthawks, least terns and even the American crocodile, Duquesnel said.
Scientists are also on the lookout for other invasive species. Recently, for example, Duquesnel was the first to document the popular Mayan cichlid aquarium fish in the waters of North Key Largo. But it's the tegu and the python that are the focus of the federal agency's attention, though the trapping programs are in different phases.
During the cooler months, tegus often hibernate, so the USGS has suspended that trapping program until March. But over the summer, the agency placed some two dozen traps between Key Largo and Florida City on the 18-Mile Stretch.
They caught approximately a dozen tegus, half of which scientists killed. The USGS fitted the remaining lizards with transmitters and then released them. They've been monitored ever since.
Though the ultimate goal is to contain the tegus' spread through the South Florida wild, the USGS is just as concerned right now with understanding the lizard, according to Duquesnel.
"Our assignment is to study behavior, movement and dispersal patterns," he said. "If we can find the Achilles heel for tegus, that is what we're looking for."
Burmese pythons are a more established and more studied problem in South Florida. So that USGS trapping program isn't seeking to learn the snake's behavior. Rather, its two-headed goal is to sample different trapping techniques and to stop the python from invading the Upper Keys.
Some pythons are already here, though they're not breeding in Key Largo yet. The first python captured in the Keys by scientists, in 2007, had the remains of two endangered Key Largo woodrats in its belly. Five pythons have been reported in the Upper Keys since August, though not all of those have been caught. It's not clear how many of those pythons were wild and how many were pets that had been released.
The USGS's 91 traps have caught just one python since Duquesnel got on the job in February, he said.
The agency had placed 46 snake traps off the 18-Mile Stretch, but those are being deactivated due to budget cuts. That leaves 45 traps in north Key Largo, which are strategically located to catch pythons in naturally occurring bottlenecks on the island.
About half of the traps sit on their own, baited with rats.
Almost daily, Duquesnel and McEachern visit those traps, where they refresh the rats' food, check for snakes and document the visits.
The 24 other traps aren't baited. Instead, they are lined up in parallel rows, separated by a fence. When the snake hits the fence, the theory goes, it will turn right or left, and slither into a trap.
The trapping program is augmented by evening road patrols, which become increasingly useful in winter months, when pythons often come out of the brush and onto the asphalt to soak up the pavement's warmth.
Duquesnel stressed that during the winter months people are more likely to see pythons on the roadways and in sunny clearings. Those who do should get a photograph then call (888) IVE-GOT1 right away and follow the instructions for a live operator. The line is always manned, he said, so if you end up with a recording, call back and listen closely to the prompts.
"We need the public to be our eyes and ears because they're everywhere we can't be," Duquesnel said.