Vance Taylor of Brooksville, Mississippi, has seen up to 50 hogs in a field at once. He estimates the animals cost him 40 to 60 acres of corn and soybeans a year. They once rooted up about 170 acres of sprouting corn; they trample ripe corn, taking a few bites from each ear.
"It looks like a bulldozer has been through your field," he said. To minimize damage, he hires a hunter and sometimes even heaps corn away from his fields so they'll eat there.
Males average 130 to 150 pounds but can range up to 250, and hogs snarf down just about anything: peanuts, potatoes, piles of just-harvested almonds. Rooting for grubs and worms leaves lawns, levees, wetlands and prairies looking like they've been attacked by packs of rototillers gone wild. Swine compete with turkey and deer for acorns, and also eat eggs and fawns.
Nor is damage limited to their eating habits. Feral pigs' feces were among likely sources of E. coli that tainted fresh California spinach in 2006, killing three people and sickening 200.
To stay even, at least 70 percent of an area's feral pigs must be killed each year, said Fred Cunningham, a biologist at the USDA's National Wildlife Research Center field station in Starkville, Mississippi. Texas alone has an estimated 2 million feral swine.
"The problem will never, ever end until they find a way to poison them," said Cy Brown of Carencro, Louisiana, a weekend hunter who estimates he has shot 300 to 400 a year for farmers.
The USDA program that began in April includes $1.5 million for the research center headquartered in Fort Collins, Colorado. Its scientists have made sodium nitrite studies a top priority.
Sodium nitrite, used as a salt to preserve meat, can keep red blood cells from grabbing oxygen in live animals. Unlike people and tested domestic animals, pigs make very low levels of an enzyme that counteracts the chemical. Swine that eat enough sodium nitrite at once show symptoms akin to carbon dioxide poisoning: They become uncoordinated, lose consciousness and die.
But baits so far haven't hit the 90 percent kill rate on penned pigs (feral or domestic, they're all the same species) needed for EPA consideration. Once it does, approval could take up to five years, Cunningham said.
One problem is creating baits in which pigs will eat a lethal dose. Sodium nitrite tastes nasty and breaks down quickly in the presence of air or water, making it easier for pigs to smell and avoid, said Fred Vercauteren, project leader in Fort Collins.
Microencapsulating the powder masks its smell and keeps it stable longer.
"We'll work on that throughout the summer," Vercauteren said.
However, there's another big hurdle: making a bait dispenser other animals can't break into.
Raccoons have pilfered one being tested. "And we'll probably have a hard time keeping a motivated bear out," Vercauteren said.