•Bill Stiver stalks wild boars after nightfall from the Appalachian Trail. He carries a Remington Model 810 12-gauge mounted with a night-vision scope and a spotting light. Sometimes he packs a .30/06 equipped with a silencer. When he finds a hog, Stiver shoots it, records its characteristics and GPS location, then hunts down another one. And he does it under the noses of 9 million tourists. Nutcase? Bacon fiend? Neither. Stiver leads the hog-removal team in the Great Smoky Mountains National Park, where, as in all national parks, hunting by the general public is prohibited. But his federally funded mandate is to eradicate the destructive, nonnative feral hog population.

Biologists like Stiver have killed hogs in the park since 1959, but Sus scrofa reproduces faster than any big North American mammal. Hogs have been spreading throughout the country, and according to experts, 50 to 70 percent of a population must be harvested annually to even make a dent. In addition to the rooting damage they cause to vegetation, hogs carry pseudorabies and brucellosis and have been known to eat fawns, calves, sheep, and turkeys.

Stiver's five-member team works from winter through early summer—sometimes camping for a week—and kills an average of 300 hogs a year. They aren't the only people allowed to hunt in a national park; last year, Hawaii Volcanoes National Park recruited hunters to control its feral sheep population. Some of Stiver's team members also hunt hogs on California's Channel Islands. "We have a huge task trying to get rid of every pig," says Stiver. "We'll probably never be done." —TYLER D.JOHNSON