EAST LANSING, Mich. — At first he thought it was a deer, perhaps the big-antlered buck he had seen before and hoped to bag someday.But the closer Steve Davenport got, the more unfamiliar the looming dark mass in the cornfield behind his house seemed.
At 15 feet, he saw the long, bristled snout. Then he saw the hoof.
“It just kept looking more and more like a pig,” he recalled. “I had never heard of anything like that. I was just kind of in shock.”
In southern states like Texas, backyard encounters with feral swine have become routine. The pigs — ill-tempered eating machines weighing 200 pounds or more — roam city streets, collide with cars, root up cemeteries and provide plot lines for reality TV shows like “Hog Hunters.”
But the pig wars are moving north. In Michigan, New Hampshire, New York, North Dakota, Ohio, Oregon and Pennsylvania — states where not long ago the only pigs were of the “Charlotte’s Web” variety — state officials are scrambling to deal with an invasion of roaming behemoths that rototill fields, dig up lawns, decimate wetlands, kill livestock, spread diseases like pseudo-rabies and, occasionally, attack humans.
In 1990, fewer than two million wild pigs inhabited 20 states, according to John J. Mayer, the manager of the environmental science group at the Savannah River National Laboratory in Aiken, S.C., who tracked the state populations. That number has now risen to six million, with sightings in 47 states and established populations in 38 — “a national explosion of pigs,” as Dr. Mayer put it.
The swine are thought to have spread largely after escaping from private shooting preserves and during illegal transport by hunters across state lines. Experts on invasive species estimate that they are responsible for more than $1.5 billion in annual agricultural damage alone, amounting in 2007 to $300 per pig. The Agriculture Department is so concerned that it has requested an additional $20 million in 2014 for its Wildlife Services program to address the issue.
There is wide agreement that the pigs are undesirable — like the Asian carp that is threatening to invade the Great Lakes, but far bigger, meaner and mounted on four legs. But efforts to eradicate or at least contain them have been hampered by the lack of a national policy to deal with invasive species as a whole, the slowness of states to recognize the problem and the bickering between agencies about who is responsible for dealing with them.
“As a nation, we have not thought through this invasive species problem, and we just have disaster after disaster after disaster,” said Patrick Rusz, the director of wildlife services at the Michigan Wildlife Conservancy. Dr. Rusz, who travels around the state educating farmers about the menace posed by the wild pigs and encouraging them to set traps on their land, is so avid a hog-hater that in the early stages of Michigan’s invasion, he went to bars to eavesdrop on hunters who might have spotted the porcine invaders.
At least in Michigan, Dr. Rusz said, the pigs appear to be winning — their numbers are estimated at 3,000 to 5,000 and growing. Wild pigs are virtual Houdinis, able to dig or climb over almost any barrier; pig experts are fond of saying that “if a fence won’t hold water, it won’t hold a wild pig.”
Allowing hunters to shoot them in the wild all year round, as Michigan and other states do, is not in itself enough to limit the population, Dr. Rusz said. So trapping is an important component of wild pig control, as are bans on owning or breeding the animals.
But state bans like an invasive species order issued by Michigan in 2011, which prohibited ownership of Russian wild boar and other feral swine, have been opposed by shooting preserves and other businesses with a stake in keeping them.
“The conundrum is that you’ve got one of the world’s hundred worst invasive animals, and at the same time you’ve got a highly desirable game species,” Dr. Mayer said. “It’s a real Jekyll and Hyde type situation with wild pigs.”
In the United States, “the pig bomb went off after 1990,” Dr. Mayer said, when Northern states began holding hog hunts, which had long been popular in Southern states. Among other reasons, the pork is tasty, hunters say. In Texas and Florida, most feral swine are descendants of domestic pigs released into the wild or hybrids. Michigan’s wild pigs came primarily from escaped Russian wild boars imported from Canada for hunting on private game ranches.
Political battles over how best to control the pigs can become vicious. In Pennsylvania, the State Game Commission was scheduled to take a final vote this month on a regulation to prohibit private shooting preserves from owning feral swine. The regulation, said Cal DuBrock, the director of the State Bureau of Wildlife Management, was intended to keep the trickle of wild pigs from turning into a deluge.
“All of our counterparts across the nation have said, ‘Nip it in the bud, otherwise it will get away from you,’ ” Dr. DuBrock said.
But state lawmakers, prodded by shooting preserve owners and some hunters, are on the verge of passing legislation redefining the term “wild animal” to exclude wild boar kept behind a fence, effectively removing them from the commission’s purview. The commission is now amending the regulation and will take a final vote in June.