Australia is struggling to control the rising population of wild pigs, which are already thought to number about 23 million. Experts in the northern state of Queensland have warned that the animals are riddled with disease and are causing huge damage to crops, as well as threatening other animals. Phil Mercer reports from the town of Mission Beach.
There are now more wild pigs than people in Australia. In the rain forests of Queensland, professional hunters like Paul Smith, an ex-soldier, are catching large numbers of these scavengers.
"Look, the pigs are a very intelligent animal," Smith said. "They've got the cognitive development of a three-year-old child so they can think and plan, and they do have a methodical approach to the way they go about their business."
Smith left the armed forces two years ago to return home to Mission Beach. That old army discipline is coming in handy in the fight against the wild pig.
"It's just like operating in a guerrilla warfare environment. I found that that military background has really helped me in my approach, looking at the problem and figuring out a way how to deal with it," Smith said. "You know, over the years I went to different places such as Somalia, Iraq, East Timor, through Southeast Asia, and again that helps coming back to your own home town like I have, and realizing that we've got a pretty serious problem here environmentally, and developing a way to combat that threat."
Tracking the pigs' movements is a tough business as trappers wade through dense forest looking for clues.
This is hog heaven. There is plentiful food and a warm climate. The pigs face few natural predators apart from crocodiles and dingoes.
All that stands between a greater surge in pig numbers in this part of the tropics is a small band of trappers.
It is the end of the line for these pigs. They are riddled with disease and worms and - sadly for meat-eaters - they cannot be eaten.
Simon, one of the boarbusters, is in charge of this part of the operation.
"Yeah, we've just placed a trap in the scrub here where people can see it sort of thing, and the pigs feel like they're protected - they're not out in the open and ? as you can see, the results are pretty good," Simon said.
REPORTER: What will happen to these pigs?
SIMON: They'll be shot, destroyed, and then placed in a pit on this farm. Yeah, this farm's got a pit, and they're put in there."
Farmers are bearing the brunt of the devastation the feral pests leave behind.
The pigs are drawn to the sweet taste of sugarcane, while their incessant foraging carves up cultivated land and uproots plants.
Farmer Terry Hampson's land is regularly invaded.
"We actually see them quite often late in the afternoon, or early morning is probably when you see most of them heading back to the national parks," Hampson said. "They're night feeders. Come through the place, roam around all night. You see quite a lot of tracks on your headlands and roadways, so we know they're there all the time. Pigs got the ability to build up very quick once they get a good source of food nearby, or they can talk to each other and tell their mates to come. They seem to get the message across pretty quick."
It rains a lot here - sometimes up to six meters a year.
The pigs dislodge soil into streams and rivers in the high country, and there is the danger it will end up polluting the Great Barrier Reef, which stretches along the Queensland coast. There are fears too that diseases and parasites the pigs carry could end up being washed into the ocean.
Environmental campaigner Keith Noble says there is broad agreement that the pigs have to be controlled.
"The feral pig problem is probably the number one issue in the wet tropics - certainly the number-one feral animal issue," Noble said. "It's also the issue where we can get a general agreement across the whole community, whether you are a farmer, a conservationist or a small land-holder. Everybody is affected by feral pigs and everyone agrees we need to do something about them."
Another big worry is that the pigs might spread infection.
An Australian government scientist, James Butler, says they could accelerate an outbreak of foot and mouth disease - a highly contagious disease that affects cattle, sheep and goats along with pigs.
"If foot and mouth was ever to hit Australia, which thanks heavens it hasn't, but if it did, pigs would be one of the major vectors for that, and given that there are almost ubiquitous everywhere and very difficult to control, they would be a major, major problem," Butler said.
It is thought the pigs were originally brought here by European settlers in the 18th century. Like other introduced species - including rabbits, red foxes and cane toads - they became an environmental disaster. Places like Mission Beach and surrounding farming areas are putting up a fight - but the battle is likely to last for many years to come.