Feral Hogs Are the Invasive Menace You’ve Never Thought About

Wild hogs destroy crops, uproot landscapes, and spread diseases—and not much is stopping them.

Think of the worst invasive species you know. Kudzu: smothering trees and houses, growing a foot a day. Burmese pythons: stripping the Everglades of small animals. Asian carp: hoovering streams clean of plankton and swimming toward the Great Lakes.

They all came from somewhere else, arrived with no natural predators, outcompeted local flora and fauna, and took over whole ecosystems. But they all have their limitations: Kudzu dies in a hard freeze, carp can’t tolerate salt water, and pythons can’t cover long distances very fast. (Thankfully.)

Now imagine a species with all those benefits—foreign origin, no enemies—and no roadblocks to dominance: One that is indifferent to temperature, comfortable in many landscapes, able to run a lot faster than you, and muscular enough to leave a big dent in your car. That describes any of the possibly 6 million feral hogs in the United States, the most intractable invasives that most people have never heard of. 

"If you wanted to create the perfect invasive species, one that could pretty much live anywhere, could eat anything, had a very high reproductive rate, was extremely destructive, and was also very difficult to control, you would have to look no further than the wild pig,” says John “Jack” Mayer, a technical program manager at the federal Savannah River National Laboratory in South Carolina, and a noted authority on feral swine. “They can live just about anywhere, from the frozen Canadian prairie provinces down to the hot, humid deserts of the American Southwest and all parts in between. They are the ultimate survivor.”

Feral hogs—or wild pigs, wild boar, feral swine, or razorbacks—aren’t new to the US; by some accounts, they arrived in the 1500s, shipped in by Spanish colonizers as a mobile meat source. Over the centuries, they settled in the forests of the southeastern US, mixing their genes with those of escaped domestic pigs and Eurasian boar imported for hunting. That ad hoc cross-breeding produced a 3-foot-tall, 5-foot-long package of razor tusks and bristles that retains the aggression of its wild ancestors while possessing the big litters and rapid breeding cycles of domestic pigs.

Which might have been fine, if the hogs had stayed in the forests. But in the past few decades, they have been on the move: through suburbs and into cities, at one point reaching 48 states. To a wild hog, modern human landscapes—farm fields, flower gardens, golf courses, landfills—are all-you-can-dig-up buffets. “Anything that has a calorie in it, they’ll eat it,” says James LaCour, the state wildlife veterinarian in Louisiana’s Department of Wildlife and Fisheries. “They’re a mammalian cockroach.”

The challenge inherent in wild pigs isn’t only the damage they do, though that is estimated to total $2.5 billion per year. Nor is it the diseases they may transmit to domesticated pigs or humans, though the dire possibilities keep biologists awake at night. It’s that there is no way of controlling them. Fences cannot hold them. Trapping and shooting can keep down their numbers only when populations start out small. And despite abundant research, pharmaceutical controls—either contraceptives or poisons, what biologists call toxicants—are still a few years away.

No one can pinpoint a single moment when wild hog populations started to explode. Will Harris grew up in southwest Georgia, where he is the fourth generation in his family to operate White Oak Pastures, a regenerative livestock farm. “Nobody here ever saw wild hogs when I was kid,” says Harris, who is 68. “Today, it’s an incredible problem. Especially for row crop farmers, the losses can be devastating, because they root and root and destroy many acres. My livestock manager and our cowboys are shooting them all the time.”

On maps kept by the National Feral Swine Damage Management Program, created by the US Department of Agriculture in 2014, the pigs’ expansion from the 1980s looks like a tide flowing inland, from the Atlantic Coast into Pennsylvania, Ohio, and Michigan, and from the Gulf Coast up through Texas and Louisiana into Missouri and Illinois. But unlike some other invasive species whose migrations have been encouraged by changing climate and weather patterns, this movement had—well, call it an anthropogenic cause. “Cable television,” says Stephen Ditchkoff, a wildlife biologist and professor in Auburn University’s College of Forestry, Wildlife and Environment.

He explains it this way: In the pre-cable years, there was occasionally a hunting show on TV. In the multi-channel era, those morphed into entire hunting channels that needed enough content to fill 24 hours every day. “And they started to show pig hunting,” Ditchkoff says. “And people said, ‘Boy, I’d like to try that.’ And pretty quickly they realized they didn’t have to go where the pigs were—they could track them, transport them, and release them close to where they lived. And that’s what led to this massive range expansion.”

The idea that people were trundling pigs all over the country might sound far-fetched, and it would have been illegal. But several lines of evidence make it plausible. Genetic studies by multiple research teams show that characteristics possessed by wild pigs in one place abruptly appear in pigs hundreds or thousands of miles away; in one 2015 study, a group of feral hogs in California possessed mitochondrial DNA sequences that otherwise had been found only in Kentucky. Then there’s the reality of how rapidly pigs appeared in new places. USDA research estimates that, on their own, hog populations will expand their range by about 4 to 8 miles per year. But Mayer jokes darkly that they have relocated at “about 70 miles per hour—which is the speed of the pickups taking them down the highway.”

And finally, there’s the paradoxical fact that when states with a new influx of hogs declared special hunting seasons or bounties to get rid of them, their pig populations actually grew—because individuals wanting to profit shipped them in to provide hunting opportunities. (Tennessee, for example, identified feral hogs in 11 counties before it declared no-limit hunting in 1999. After the program ended in 2010, hogs were documented in 70 counties.)

Between people seizing hunting incentives and hogs learning hunters’ habits, sport hunting has not made a long-term difference in how many feral pigs there are. “It’s counterintuitive to think, but hunting is not the solution to the existence of feral swine,” says Michael Marlow, a wildlife biologist and assistant program manager at the USDA’s national program. “We don’t discourage the harvest of feral swine by hunters opportunistically. But we don’t see it as a tool that’s going to solve this problem.” 

Since its founding, that USDA program has worked to reduce wild pig populations through a combination of trapping and euthanizing groups of swine, and encouraging legislation that prevents the animals from being replaced. That has led to eliminating wild hogs in seven states—colourado, Maine, Maryland, Minnesota, New Jersey, New York, and Idaho—and reducing their numbers in Iowa, Vermont, Washington, and Wisconsin. But that leaves at least 35 states where they still flourish, though Texas allows hunters to machine-gun hogs from privately operated helicopters. (In the Carolinas, federal agents use copters as well.) Pigs, as the saying goes, are smarter than dogs. Hunted during the day, they will switch to foraging at night. Hunted with traps, they learn to recognize and avoid them. And hunting with aircraft taught them pretty quickly to recognize engine noise and take cover.

Thus, in Louisiana, feral hogs continue rooting up levees, wrecking crawfish ponds, chomping alligator eggs, and digging out coastal marsh plants, which lets the ocean wash land away. In Texas, where there are about 3 million wild pigs, authorities price just the agricultural damage at more than $500 million per year, from destruction of row crops and rice fields to predation on small livestock such as lambs and goats. A study published last year by researchers at Texas A&M University estimated the damage to Texas golf courses and cemeteries at more than $1.6 million per year.

That’s not counting the human costs. Texas is the only place in the US where someone has been killed by wild hogs: In 2019, a home health care aide going to work before dawn was attacked by a group and bled to death. Wild pigs carry a raft of diseases that imperil the enormous US domestic pig herd, and some threaten other species also—hunting dogs, and also an endangered Florida panther, have died of hog-transmitted pseudorabies. They also carry diseases that affect humans, including brucellosis, which has sickened hunters and veterinarians, and leptospirosis, which has infected triathletes and adventure racers. 

Wild pigs are also concerning because of the diseases they might transmit, but haven’t yet, says Vienna Brown, a biologist with the USDA national program. Pigs have long been feared as a mixing vessel that allows human, swine, and avian types of influenza to combine into human pandemic strains. Wild hogs are also at risk of African swine fever, a lethal disease that already has moved from Europe to the Caribbean, and would completely shut down the US pork trade if it infected domestic pigs.

And above all that, they’re a road hazard. An adult pig can weigh at least 200 pounds, and they possess a weird anatomical quirk: Their eyes don’t shine in the dark. “I drive about 40 miles each way to work,” says Michael Bodenchuk, a biologist and state director for the Texas Wildlife Services program, who is based in San Antonio. “And at least once a month I go by a road-killed pig. And 100 yards along I see the car that hit him.”

Between the reality of the threats and the inadequacy of hunting to reduce them, the search is on for a big solution. Contraceptives would be the least invasive; they could bring down the number of litters a sow has or the number of piglets in a litter, or impair the fertility of boars. But so far, no one has successfully developed an oral contraceptive that could be put into feed and distributed in the wild, and that could deliver a reliable-enough dose over time.

That leaves pharmaceutical intoxication—poison, basically—as the only workable option for reducing pig populations. None are legal in the US yet, but researchers have pursued two paths to find one. The first is warfarin, which humans take in small doses as a blood thinner and pest control companies use in much bigger doses to kill rats. Administered to hogs, it causes them to bleed to death internally. One warfarin product was briefly field-tested in Texas in 2017, but the product was quickly opposed in court by hunters and meat processors, and the company making it backed down.

The second is sodium nitrite, a salt used to cure cooked meat products because it inhibits the growth of pathogenic bacteria. (Butchers call it “pink salt,” but it is not the pink Himalayan salt-block kind.) In high-enough doses, it prevents blood from carrying oxygen; when given to hogs in field bait, they stumble, become comatose, and die. That seems like it might be more humane than inducing hemorrhaging, but researchers haven’t been able to achieve a feeding regime that guarantees only hogs will take the bait and not smaller animals or birds. And neither line of research has solved the problem of collecting the hog carcasses afterward, before other wildlife eat them and possibly are poisoned in turn.

Some academics and companies continue to research toxicants, but they are careful to say that achieving a successful, licensed product won’t solve the wild hog problem. “It is a common misconception that having an approved toxicant or contraceptive will be a silver bullet,” James Beasley, a professor of wildlife ecology at the University of Georgia who studies toxicants, told WIRED by email. He estimates that any approval is still several years in the future, and adds: “In reality, if and when any pharmaceutical product is approved for use in wild pigs, it likely will just become another tool in the toolbox.”

Envisioning toxicants in use, though, assumes the public will accept them—and as the legal reversal in Texas shows, that is not guaranteed. “The US has never warmed up to poisoning wild living animals,” Mayer notes. It’s entirely possible, he says, that some people enjoy wild pigs as free-living animals or features of the landscape, and would be opposed to poisoning them. That would make their properties islands of survival, sheltering pigs who could repopulate cleared areas after elimination programs end.

This means the future for wild pigs likely is not eradication. It might be reduction, knocking their numbers back so ecosystems can recover before populations surge again. “States in the Southeast have had these animals since the 1500s,” Mayer points out. “We may just have to learn to live with them.”

Feral Hogs Are the Invasive Menace You’ve Never Thought About

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