Hogs Gone Wild
Will feral swine, an extraordinarily invasive species, invade Minnesota? Only if we’re unable to outsmart the pigs.
In early March of 2016, amid the mature aspen forest, grasslands, and wetlands of West Valley Wildlife Management Area in far northwestern Minnesota, piglets were born. Their mother had wandered off a nearby farm with other pigs and gone feral—begun living in the wild—when she gave birth in the WMA. Though the births were at first undetected by humans, they soon came to light and achieved dubious distinction as an extremely rare instance of feral pig reproduction in the state—and on designated wildlife lands, no less.
The incident struck a chord among Minnesota resource and wildlife experts whose role is to guard against invasive species like feral swine. Minnesota is fortunate not to have a self-sustaining population of feral pigs, but many other states do, and their problems inevitably began with only a few hogs. In this case, the Minnesota system of hog prevention did its job.
Captain Pat Znajda of DNR Enforcement, then a lieutenant and district supervisor, responded to the initial call about the loose pigs in Marshall County in March 2016. He learned from a neighbor that the animals belonged to a landowner who didn’t live on site. Znajda contacted the owner, who told him the swine had been free roaming for at least a year.
Znajda informed the landowner that it’s illegal, under Minnesota Statute 97A.56, to possess, release, or allow feral swine to run at large. When Znajda revisited the site a week later, he found a new but clearly inadequate fence: a double strand of barbed wire 40 inches off the ground, with “swine going in and out of the fencing,” he wrote in an incident report. He warned the owner that the pigs could be eliminated if they remained at large.
They did. The mother sow on WMA land was soon tracked, found, and shot by USDA Wildlife Services removal specialists, which was when the recent piglet births were discovered. Wildlife Services returned that October and shot four more pigs on private property in the area. The pigs’ owner was cited, convicted, and fined $135 for a feral swine violation. Although the incident was resolved and a booming wild pig population averted, it sent a warning sign: What if those pigs hadn’t been reported and found until more roaming and more breeding and more births had occurred?
“That Marshall County [case] kind of made you realize that, wow, we documented that the pigs were loose and living on their own for quite some time, and had actually reproduced in the wild,” says Gary Nohrenberg, Minnesota director of USDA Wildlife Services, which removed the pigs. “And it’s not hard, with even a little imagination, to realize how they could have become established deep into a fairly remote WMA and thrived for quite some time before someone ran across them.”
Smart and Invasive. They’re intelligent, they’re elusive, and they’re destructive on the landscape. Pigs living in the wild—feral hogs—are spreading across North America, trampling, foraging, wallowing, and rooting up land as they go. They are fouling springs and streams, disturbing native plant and animal habitat, eroding soil, and otherwise damaging public and private land, including cropland, to the tune of more than $1.5 billion annually. They can spread diseases that could cross over to domestic pigs. They are an extraordinarily invasive species with hooves, tusks, and a long track record of damage wherever they’ve gone.
No member of the swine family, Suidae, is native to North America or, for that matter, to the entire Western Hemisphere. Whether you call them pigs, hogs, boars, razorbacks, or swine—domestic or wild—they all originated on the other side of the world from Minnesota.
Minnesota natural resource managers, feral swine experts, and hog farmers all fear repercussions and damages if we don’t take the right steps to keep feral pigs from setting up shop here.
“They’re a threat to resources,” says Eric Nelson, wildlife animal damage program supervisor at the Minnesota Department of Natural Resources. “If you look to southern states, the damage that they can do is astronomic, not only to natural resources but to agricultural producers.”
There are more than 6 million feral pigs in the United States, according to the USDA. In 1982, pigs were living in the wild in 544 counties in southern states from east to west. By 2020, they had spread to 1,915 counties, moving inland and northward, with small pockets as far north as the Upper Peninsula of Michigan and in North Dakota near the Canadian border. At the same time, a population of hardy Eurasian boars is expanding in Canada, with a lobe reaching down ominously toward Minnesota’s northwest. As feral swine move into new territory across the continent, resource managers are taking on extra expense and effort to deal with them, and residents in those areas are learning that wild hogs often don’t make good neighbors.
“They’re considered one of the most aggressive invasive species that we have on the landscape,” says Nohrenberg of Wildlife Services. “The potential is there for them to make a big impact in a short amount of time if they’re unchecked.”
A self-sustaining population of feral pigs could become established in Minnesota in several different ways. They could come from pigs that escape captivity, a regular occurrence across the state. They could come from hogs that are intentionally released, which has occasionally happened. Or they could simply walk or swim in from a population in a bordering state or province.
Because pigs reproduce prodigiously—females can give birth at 6 months old and can produce two litters of 4 to 12 piglets a year—their numbers can grow exponentially if unchecked.
“You just can’t leave a single female and a single male on the landscape,” says Alan Leary, state feral hog coordinator at the Missouri Department of Conservation. “If they’re out there for a year those two could become 30.”
Missouri has seen the damage that feral swine can do to wildlife and habitat.
“You know the old term ‘sloppin’ the hogs,’” Leary says. “Hogs eat anything they come in contact with. They’ll eat the nests of ground-nesting birds, they’ll eat reptiles and amphibians, they’ll occasionally take a fawn deer. They will compete with our native wildlife for acorns and food sources.”
Missouri conservation staff have had to fence off a federally threatened plant species, Mead’s milkweed, from feral hogs, and Leary is concerned about the federally endangered Hine’s emerald dragonfly, which lives in the distinctive wetlands called fens. “If hogs get into a fen, they can tear up a fen pretty bad,” he says.
Pigs change soil chemistry when they turn soil over with their rooting and foraging activity, says Dwayne Etter, wildlife research specialist at the Michigan Department of Natural Resources.
“We have a lot of high-quality streams and rivers in Upper Michigan that are really prized by our trout fishermen in particular,” he says. “And we’ve had concerns that [feral swine] would change the water chemistry in those environments if we got enough pigs on the landscape.”
Etter too cites potential impacts to vulnerable species, especially in wetlands. “A lot of the threatened and endangered species are dependent on wetlands, and these pigs have a high affiliation for those wetland areas.”
It’s not just the natural world that takes a hit from feral pigs. Commercial agriculture suffers too. “They do tremendous damage to agriculture,” says Etter. “A sounder [group] of 15 or 20 hogs can easily destroy 10 acres of corn in one night.”
Hog disease that could devastate the U.S. commercial hog industry is also a serious concern because some diseases can cross between domestic and feral swine. Scientists have detected pseudorabies, a disease eradicated in 2004 in the U.S. commercial swine herd, in Michigan feral swine, says Etter, and African swine fever is an ever-looming threat for hog producers.
“It becomes a really big issue if we get a foreign animal disease established in the feral swine population in the U.S.,” says Beth Thompson, executive director of the Minnesota Board of Animal Health. “Not only does that affect international trade for our commercial herd; it is also going to be close to impossible to eradicate a foreign animal disease in that [feral] population.”
Incredible, Adaptable Pig.
Pigs, even ones raised on farms, can adapt much more easily than one might think to live and thrive in wild places.
“Pigs are smart,” says Thompson. “They can figure out how to overwinter. They can figure out in times of drought or other weather events where they need to go to bed down. Where to get their food, where to get their water. All of that.”
A common misconception is that pigs undergo a dramatic physical transformation when they go feral. But “there’s no difference when you start getting morphological,” says Nelson of the Minnesota DNR. All pigs have tusks, though the tusks on domestic hogs are sometimes docked, and all pigs grow hair. “You can’t just look at a pig and say, ‘That’s feral swine,’” he says.
Genetically, all swine are descended from the same Eurasian boar relatives, but regional differences among North American feral swine populations are emerging from new science.
In Michigan, says Etter, genetic analysis by researcher Timothy Smyser has shown that the majority of feral swine sampled were Eurasian boars or Eurasian boar hybrids (sometimes called Russian boars or Russian boar hybrids). This is in line with other research showing that feral swine in more northerly states, and in Canada, have more boar genetics than those in southerly states, which “have a lot more domestic pig in them,” he says.
Home-range studies done with tracking collars show that northern swine with more boar genetics can roam farther, especially in winter conditions. Males ranged over more than 22 square miles and females covered about 7 square miles in winter in a Michigan study, says Etter, compared with ranges under 3 square miles for males and under 2 for females in typical southerly locales.
“When you think about trying to locate and remove animals in those large wetland complexes that we get in northern Michigan, northern Minnesota, now you’ve got an animal that covers a lot more ground. It’s just harder to find them.”
And as the Minnesota WMA pigs show, they can even live alongside large predators such as bears and wolves. One trail camera placed by Wildlife Services showed a wolf in the same area as the feral pigs.
“When they removed the sow that came in to their bait pile,” says Nelson, referring to the Wildlife Services crew, “they went and found 3- to 4-week-old piglets still in there. She’d fought off wolves and other animals, living out there in the wild in February and March in subzero temperatures and deep snow. And those were pigs that were being raised for food!”
Wherever loose pigs come from, and whatever type of genetics they have, they all pose an equal hazard to Minnesota lands, natural resources, and agriculture, says Nelson.
“A feral swine is a feral swine,” he says, “and it needs to be removed. They all have the same impact and threat.”
Who Let the Hogs Out?
Currently, Minnesota’s feral hog problems are basically temporary loose pig problems. Few escaped hog reports in Minnesota end up like the WMA incident, poised to unleash a new feral population on wild lands. Most cases are more mundane stories where pigs briefly escape captivity in less remote areas.
That doesn’t make our feral hog control experts any less vigilant. The Minnesota Department of Natural Resources, the Minnesota Board of Animal Health, and USDA Wildlife Services are the three entities jointly in charge of feral hog control in the state. The Board of Animal Health prohibits the importation of feral swine, guards against swine disease, and assists hog owners in keeping their pigs fenced in. The DNR investigates feral hog reports that come in through conservation officers, local law enforcement, citizens, and other channels. And USDA Wildlife Services gets involved to eliminate feral pigs when the Board of Animal Health can’t identify their owners and the DNR requests monitoring and removal.
Representatives of this wild pig triumvirate, dubbed the Minnesota Feral Swine Working Group, meet regularly to stay up to date on hog issues, and they confer whenever a case is considered for lethal resolution via Wildlife Services removal specialists. This step is taken only when all three parties collectively agree on its necessity, which happens a handful of times each year.
“Oftentimes we’re called in as kind of the last resort,” says Nohrenberg.
About a dozen times a year, on average, loose pigs are reported in Minnesota. There’s no “typical” escaped pig report, says Nelson. A call can come from a rural area, a suburb, or a city. “We’ve had them on the edge of Rochester, we’ve had them down in Shakopee,” he says. Most reports, Thompson says, involve “some defect or failure of fencing—or human failure to watch the fence.”
Virtually no reports come in from large commercial hog facilities where confinement is the name of the game. Smaller hog farms are more likely to lose a pig or pigs now and then. And people who are new to keeping pigs, like owners of pet potbellies or locavores trying to raise their own food, sometimes underestimate the abilities of pigs to break free from the confines of the pallet fence whose design they got off the Internet.
Potbellies pop up regularly among escaped pigs, say those who deal with feral swine in Minnesota. In fact, one literally popped up and spooked a farmer in the dark near his cow pasture, says Mackenzie Reberg, a veterinary officer at the Minnesota Board of Animal Health who investigated the case and warned the owner to keep her potbelly penned up.
In 2009 in southwestern Minnesota, a “handful” of potbelly pigs were released on private land, began breeding, and soon grew to more than 50, predating the WMA pig reproduction by several years, before they were shot by local law enforcement. This was before Minnesota had a feral swine statute and before the DNR was tasked with hog control.
Now, any escaped pig incident in the state is logged as a feral hog report, and that’s important: Such reports establish a record that is used in part to determine Wildlife Services funding for the state from the National Feral Swine Program, which was established in 2014. States with the worst wild pig problems, classified as level 5, get the most help, while those with the lowest, level 0, get none. Minnesota has since 2017 been a “detection” state, existing in a limbo-like classification above 0 but not yet at 1.
Both Nelson and Nohrenberg express concern about federal funding levels, which could potentially cut off money to detection states that report no feral swine for two years, causing those states to backslide on hog control. “It’s important for us to stay in the game, to respond to the types of damage that we know does occur and could occur from even loose domestics,” says Nohrenberg.
Pig Prognosis. There is some good news on the feral hog front. Since 2014, when the national program began encouraging and helping states tackle their feral swine problems, several states have cut back their feral swine ranges and numbers. And overall feral swine population numbers in the United States have decreased due to “statewide elimination efforts,” according to the USDA.
This success is no reason for complacency, say the experts who deal with wild hogs in other states. Asked for words of advice for Minnesotans staring down an uncertain feral swine future, Etter, from Michigan, urges awareness and vigilance.
“The first thing is just to recognize how detrimental these animals could be to native wildlife,” he says. “Once they become established, it’s extremely difficult to remove them all. And even having small numbers can become big numbers really quick.”
Missouri’s Leary, whose state deals with feral hogs on a scale that Minnesota aims to avoid, echoes the sentiment.
“Commit the resources to prevent the problem from getting started,” he says. “It would be a lot less expensive and a lot easier to prevent it than to have to try to eliminate them after they become established.”
Hold Your Fire
Legalizing hunting is no silver bullet for feral swine.
It’s illegal to hunt feral swine in Minnesota under Statute 97A.56. “We don’t want people to shoot pigs; we want them to report them,” says Eric Nelson of the Minnesota Department of Natural Resources. If someone does shoot a pig, they need to surrender it to the DNR within 24 hours or they can be prosecuted for hunting feral swine.
So ... if feral hogs were to become established in Minnesota, couldn’t we just legalize hunting them? We’d have another game animal to pursue, and we could make bacon!
Not so fast. There are many good reasons why hunting is a particularly poor solution to feral swine problems and can in fact even exacerbate them. Here are the top strikes against it:
Hunting teaches pigs to avoid humans.
Pigs are social animals that in the wild live in groups called sounders. Citizen hunters might pick off, say, one or two pigs from a sounder of 20, but that will only teach the remaining pigs to be even warier of humans. And “with the reproductive rate of feral hogs, that’s just not going to do any good,” says Alan Leary of the Missouri Department of Conservation.
In Minnesota, USDA Wildlife Services state director Gary Nohrenberg is in charge of the professionals who track down and lethally remove escaped hogs when necessary. Their goal is to remove the entire sounder at one time.
“They’re an intelligent species, and it seems like they can smell gun blue at about one mile once they’ve been shot at,” says Nohrenberg, referring to the oxide coating used on firearms. “So they become very leery, and that’s one of the reasons that we’d prefer people not shoot them. The risk is that they potentially would break up a sounder and maybe even disseminate or spread the pigs even further.”
Allowing feral swine to be shot incentivizes the illegal release of pigs on the landscape.
The killing of hogs was wholly unregulated in Missouri prior to 2016, and the state saw “a lot of intentional releases,” says Leary. “There’s very clear evidence that people were releasing hogs to create more hunting opportunities.”
From the mid-1990s, when Missouri starting having feral hog issues, until 2016, when hog hunting was banned on lands owned, leased, or managed by the state, “the hog population continued to grow quite significantly,” says Leary. The state now depends on full-time trappers to control hogs.
Missouri has made a nod to swine hunting, though: It’s now legal, if you’re hunting deer or turkey in season on state lands and have an unfilled deer or turkey tag, to opportunistically take one feral hog.
Hunting encourages the release of destructive breeds.
When hunting is the goal, illegal hog releases are more likely to be Eurasian boars or Eurasian boar hybrids. These breeds, while more sought by hunters as the epitome of the wild boar, are even hardier and potentially more destructive on the landscape than escaped domestics.
Hunting is not an effective way to control feral hog populations.
Hog hunting is legal in Michigan. Is it helping the state reduce its feral hog population? “No, it’s not,” says Dwayne Etter of the Michigan Department of Natural Resources. “Even in the states that have high feral pig abundance, hunting has no impact on those populations. It’s been shown repeatedly.”
“Hunters just can’t make the effort necessary to reduce enough animals,” adds Etter. Operating as recreationists, they can’t match the well-honed tactics of trained professionals—and moreover they don’t want to.
Says Leary from Missouri: “Anybody who hunts knows that you’re going to go hunt where the population of whatever you’re hunting is high. And if that population is reduced, you’re no longer going to hunt there. Nobody’s ever going to call you up and say, ‘Hey, I’ve got a horrible spot for hunting hogs, I’ve never seen one there in five years, you want to go hunting there with me?’
“When the goal is elimination, you continue to remove the animals until the very last one is gone. And that’s just not generally how it goes when you’re hunting.”
In Missouri, 48 full-time trappers—16 for the state and 32 for USDA Wildlife Services—have learned the ways of the pig well enough to trap large numbers at once in baited, penlike traps. “We had a guy who, with one drop of the trap, got 72 hogs at one time,” says Leary. “That’s what we need to do. Hunting doesn’t do that.”