麻豆传媒

RODNEY WOODSON never set out to be a pig trapper. He joined the because he was passionate about conserving water birds. But that was before the hogs rocked up, with their high libidos and low cunning.

Across the world, and especially in the southern US, feral pigs are a problem. Marauding hordes of swine are destroying crops and sensitive natural environments, causing traffic accidents and spreading disease and parasites. They have even dug up cemeteries. The US Department of Agriculture estimates the damage at $1.5 billion a year.

As so often with invasive species, this is a problem of our own making. Wild pigs were introduced to the US by Spanish settlers hundreds of years ago, but weren鈥檛 a cause of widespread concern until the 1990s, says zoologist Jack Mayer at the in South Carolina, when cable TV ads began promoting the animals as an exotic alternative hunting target to turkeys and deer. In 1999, Tennessee established a hog hunting season, and soon enterprising landowners were stocking up. That ushered in 鈥渁n explosion of new hog populations鈥� across the state, says Chuck Yoest, coordinator of the , part of the agency that Woodson works for. In 2011, the state reclassified pigs from big game to destructive pests.

The pigs鈥� supercharged reproduction rate isn鈥檛 helping. A sow may produce two or more litters of typically five or six pigs every year, making it nearly impossible to cull all the individuals in an area at once. Pig population models show that clearing an area requires removing 70 per cent of the animals 鈥測ear after year after year, until you drive that population to extinction鈥�, says Mayer.

In Texas, some landowners now offer wealthy customers the opportunity to machine-gun pigs from a helicopter for as much as $1000 an hour. Other communities have called in teams of sharp shooters. But critics say that these methods of pig control are not just inhumane, but ineffective. For a start swine are fast: they can run at up to 50 kilometres an hour. They can also , for example switching between nocturnal and diurnal living patterns. 鈥淭hey鈥檙e a pain in the backside, but they are interesting critters,鈥� says Mayer.

Traps of the sort Woodson lays are generally thought to be the least bad option in dealing with the pigs. But porcine intelligence makes trapping a full time job. , are whizzes at navigating complex mazes and can manipulate cursors on a screen by controlling a joystick with their snout. It means in simple traps they soon work out how to jump over short fences and climb taller ones, for example by gaining purchase at a corner.

Boar busting

Woodson鈥檚 first tactic was to play the long game and put the pigs under surveillance. He installed cameras near baited traps, so pest control officers could examine pictures to see how many animals came by, and when. Once they knew which traps were frequented by the hogs, they could stake them out, hiding near a trap and triggering its gate at the right moment.

This was by no means a perfect strategy. It took lots of time and people, and although pigs can鈥檛 see well, they have a keen sense of smell. If they picked up the scent of a human, the pigs wouldn鈥檛 approach a trap.

So in his latest iteration Woodson has gone wireless, using solar-powered cameras overlooking a circular enclosure with 1.4-metre-high fences 鈥� high enough for pigs to have trouble climbing them, and with no corners to aid escape. When a motion sensor detects a pig-sized animal, it sends Woodson an email. From his own home, he can watch a real-time feed of the trap and at the right moment flip a switch to drop the gate.

This human check is critical, Woodson says. If even one pig from a group is left uncaught, it may learn to avoid similar traps. Though maternal education in pigs hasn鈥檛 been studied rigorously, Woodson鈥檚 experience suggests that if it鈥檚 a sow, it may train its offspring to do the same.

His creative trapping is bearing fruit: the record for one of the traps is 52 swine at once. And the wireless approach is generally becoming more popular. Landowners can buy commercial versions of remotely operated traps, including the $6000 Australian model known as the .

But the story is far from over. Eager for more game, a few unscrupulous landowners are still trafficking pigs to Tennessee from neighbouring states, creating fresh pockets of infestation. Longer-term, climate change may also exacerbate things, at least in Europe. Last year, researchers at the University of Veterinary Medicine in Vienna, Austria, predicted that feral pig numbers there , as more food becomes available.

So others are thinking beyond traps. There is the , in which, when a group of pigs is culled, a sow is left alive and tagged with a GPS collar. She then does the hard work of finding another, doomed, tribe 鈥� at which point shooters are sent in. Then there are chemical approaches such as hog-specific poison or contraceptives. Later this month, trappers and conservationists will brainstorm new ideas in Myrtle Beach, South Carolina, at the international .

Meanwhile Woodson can鈥檛 stand idle. His latest trap has an oblong pen with two gates directly opposite each other, giving the pigs the illusion of a safe passage. The hogs in his patch are wise. It is a brutal business, and there鈥檚 no time for complacency.

This article appeared in print under the headline 鈥淵ou swine!鈥�