Jeff Fobb freezes as he tries to sort through the noises rising from the swamp of the Everglades: the beating wings of an ibis, the scurrying of a lizard, the much louder splash of an alligator lowering itself into the water or, the sound he really wants to hear, the rustle of a large python in tall grass. "It sounds sort of like the wind, but more steady," says Fobb. He combs through the grass with a long metal hook. No snakes.

But the pythons are out there, somewhere, and Florida is looking to men like Fobb, a ponytailed former marine who heads the Miami-Dade fire department's venom bureau, to hunt down and kill them.

Armed with a hunting knife, insect repellent, and mesh laundry bags into which he is hoping to bundle his prey, Fobb is on the frontline of a new push by Florida to try to contain a population explosion of alien intruders that is threatening the ecological balance of the Everglades and frightening the public in surrounding farm lands.

The state is in the midst of its first-ever open hunting season on pythons. Authorities say the hunt, which runs until mid-April, could be a last chance to get rid of the snakes before they do irreparable harm to some of the endangered species in the Everglades.

Nobody knows how many pythons or other large constrictors are on the loose, or exactly how they got out into the wild. Estimates run as high as 100,000. State wildlife officials are hoping a significant slice of the population froze to death in February's extreme cold spell but they admit their evidence is spotty.

"The only safe thing to say is certainly at one time there were thousands," said Scott Hardin, head of exotic species for Florida's Wildlife and Conservation Commission.

Conservationists and wildlife officials believe the snakes are the offspring of unwanted pets that were dumped in the wild. Hardin thinks they may originate from a breeding farm that was torn apart by Hurricane Andrew in 1992, flinging snakes through the air.

What is clear however is that they are an increasing public menace. Full-grown, a Burmese python is 200lbs of sinuous muscle and can overpower any animal in the Everglades.

According to a food pyramid of the python diet put together by Everglades National Park, pythons have eaten animals ranging from raccoons to blue herons to alligator.

They are multiplying: a mature female python lays up to 100 eggs a year. Fobb's Venom Bureau responded to 90 snake emergencies last year, mostly from pythons.

And they may be on the move. A study by the US geological survey suggested the Burmese python could begin moving out of south Florida, potentially even to other US states.

The hunt is the latest attempt in a series of efforts by government agencies and environmental organisations over the last decade to try to limit their numbers.

In 2008 state authorities brought in a law requiring python owners to implant their snakes with a computerised chip. This year the Obama administration proposed a ban on the import or transport within states of the Burmese python and eight other large constrictors.

Now state officials have decided to call in hunters to rout the intruders. Aside from bragging rights, hunters could sell the skins of their prey, which go for about 10 dollars a foot.

Fobb though is more focused on getting to know the enemy. He carries a notebook in which he enters the animal's length, weight, sex, and stomach contents before what he calls the "unhappy denouement": decapitation by pithing, the insertion of a thin wire in the snake's spinal cord. The carcasses are tossed back in the wild.

But getting rid of the creatures is proving more complicated than had been expected. To date, none of the 60 hunters who signed on to a special course on python tracking have killed a single snake in the areas surrounding Everglades National Park approved for the hunt. The national park itself is off-limits to python hunters.

Kenneth Krysko, a senior scientist at Florida's Museum of Natural History, argues that is because the hunters are looking in the wrong place. They need to go deeper into the Everglades – perhaps within the borders of the park itself – to get their prey.

"The commission is essentially just sending guinea pigs out into the wild just to see if there are pythons in those areas," he said. "They are found in very remote areas — eight to 12 miles away from the nearest road. It's pretty obvious that we will never be able to exterminate those individuals."

Even Hardin admitted that the hunt was not going entirely to plan.

"It's going to take a while for them to get the hang of where to look," he said.

Fobb too has failed to find a single python on three forays in March, though he still gets daily calls at the venom bureau.

"It's hard work. It's not something where you just come out and have a wholesale slaughter in a couple of weeks," said Fobb. "You just have to keep coming out and looking."

Sometimes though, the snakes come looking for you. After a six-mile trek through the Everglades recently, Fobb got a call from home. He and his wife live on a few acres with horses, donkeys, dogs, and chickens and – as of that morning – a nearly nine foot python coiled up beside their house.

By the time he reached home, the snake was safely caged in a dog kennel. "I just dragged him out by the tail. He tried to bite me and pooped on me and everything," said his wife, Sandy. "Don't you be letting that sucker loose in my house."

Fobb sighed. "I should have just stayed home."