The snake hunter shakes his head as he crouches over a sandy trail that pushes through Collier-Seminole State Park.
Hoping to spy subtle signs of his slithering prey, Paul Andreadis instead finds only pebble-sized pockmarks left by raindrops overnight and maybe tracks left by a deer, probably that morning.
"No, nothing here," said Andreadis, a snake researcher visiting Collier-Seminole recently from Denison University, located near Columbus, Ohio.
Andreadis stands up and, from behind the mosquito netting hanging from the brim of his wide-brimmed hat, sets his sights on the trail ahead.
He knows Burmese pythons are out there; a half-dozen of the nonnative reptiles have been spotted since 2003 at the state park along U.S. 41 East as they have spread west from a stronghold in the Everglades.
The question scientists are trying to answer is whether Collier-Seminole has a breeding population of the big, fat predators.
"If we do, we've got a fight ahead of us," park biologist Maulik "Mo" Patel said.
The fight already is on at Everglades National Park, where the first python was found dead on U.S. 41 in 1979. The first baby python was found in 1995, and rangers found the first nest of python eggs beneath an overturned wheelbarrow in 2006.
Based on the density of Burmese python populations at a national park in India, researchers estimate there could be at least 30,000 pythons crawling around the park.
The invasion is thought to have begun with the release of unwanted pet pythons into the wild. Baby pythons measure 20 inches long, but within a year reach lengths of 5 feet. Full-grown pythons come in at 20 feet or more and can weigh 200 pounds.
Their voracious appetites make them a threat to the South Florida food chain, which isn't built with a link for nonnative pythons.
They have been known to feed on everything from bobcats to birds. The discovery a couple years ago in the Everglades of a python that had burst open after swallowing an American alligator raised the concerns to a new level.
Key to fighting back against the pythons is learning more about their habits, scientists say.
They have implanted radio tracking devices in 17 pythons and rereleased them into Everglades National Park to try to discover their hangouts.
With that knowledge, scientists can lay traps to catch even more of them.
Scientists also are experimenting with chemical attractants and are using a beagle, nicknamed Python Pete, to ferret out the sneaky beasts.
The first python sighting at Collier-Seminole, near the park entrance in 2003, coincided with an upswing in the numbers of pythons taken out of Everglades National Park, according to Interior Department figures.
What started out as a dozen or so a year in the 1990s ticked above 50 in 2003 and soared to 250 in 2007, figures show.
The sightings at Collier-Seminole have been clustered along the park's western edge, where a canal, a tall berm and plenty of Brazilian pepper make for prime python habitat.
One was found as it tried to escape a prescribed burn at the park; rangers spotted two adult pythons crossing the bottom of a dried up canal but were unable to pin it down. A mower got it later, park biologist Patel said.
In April, firefighters plucked an 8-foot python out of the rafters at a hangar at Marco Island Executive Airport.
Pythons usually aren't so obvious.
"The whole lifestyle of a snake is built around being secretive," Andreadis said.
Pythons are more likely to be found during the winter, when cooler weather chases them out of their hiding places to bask in the sun.
Sightings are at their lowest in July and August, according to records from Everglades National Park, but Andreadis hoped to even the odds by driving the roads in and around the park overnight.
But if there are baby pythons to be found at Collier-Seminole, early August is a good time to find them, he said. That's because pythons hatch between late June and August from nests where mother pythons have been coiled around clutches of between 30 and 50 eggs.
Nesting sites in Collier-Seminole might be susceptible to summertime flooding, which would explain why rangers have found no signs of a breeding population, Andreadis said.
A pig frog snorts as Andreadis wades waist-deep into an overflowed canal at the state park and disappears behind a wall of tall grass.
A few minutes later, he climbs back into view over a nearby berm. No python.
"You'd be surprised how well a 15-foot snake can hide, squirreled away in the vegetation," Andreadis said earlier.
Andreadis, who calls himself a "bona fide science geek," has been waiting 20 years to come face-to-face with an adult python in the wild.
As a graduate student at the University of Florida, Andreadis had planned to study Burmese pythons in their native habitat in India, but the trip was canceled amid political turmoil.
So the 1,200-mile drive from central Ohio to South Florida is part nostalgia, part unfinished business trip for Andreadis.
Scientists might never be able to call off the hunt for pythons in South Florida.
"The price we pay may be eternal vigilance," Andreadis said.