It was almost 2 a.m. on a moonless October night at a ranch in Caldwell County, just northeast of San Antonio. I sat next to Eli Smith in his small utility terrain vehicle, the engine off. Behind us, the cargo bed held a kennel containing six dogs he had trained to track feral hogs. Smith is a large man with a keen appetite for killing invasive swine—he hunts them as often as four days a week. “I kill ’em any way I can,” he told me. “I shoot ’em with the AR-15. I set the dogs on ’em and catch ’em and stick ’em with the knife.” He prefers the second method, which hunters call pig stickin’.To my right sat Smith’s friend Patrick Plant, clutching…