Feral Swine Wreak Havoc

Feral swine in a forest


As pests go, wild pigs are huge – and hugely effective.

They damage just about every type of crop they encounter and cost growers even more in control costs and property damage. They carry diseases that can be transmitted to domestic livestock and humans, damage rangeland as well as crops, and have spread from a handful of states in the 1980s to 37 states now.

“They can pretty much live anywhere in the lower 48 states,” explained Nathan Snow, a wildlife biologist at the National Wildlife Research Center in Fort Collins, Colorado. “And they’re spreading pretty rapidly.”

The center’s 43-acre campus is the research home of the Wildlife Services program of the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service. Its research supports the National Feral Swine Damage Management Program and ongoing efforts to control wild pig populations.

In the West, California has been hit hardest by feral swine, but eastern New Mexico and areas of Colorado, Arizona, Nevada, Utah, Oregon and Washington also have feral swine populations.

Regionally, the south has the most extensive problem, with feral swine reported in nearly every county from Texas to Florida.

“The populations are pretty dynamic,” Snow explained. “A group of pigs is known as a sounder, and while those average seven to nine individuals, they can have up to 50, led by a dominate female. The big boars are more solitary and will be with one sounder for a while then with another.”

And when Snow says big, he means it. The biggest boar the center put a GPS tracker on weighed 300 pounds, and most adults range from 75 to 200. And while the size of the sounders and individual pigs varies, there is one constant.

The rooting, wallowing, omnivorous pigs will be destructive.

A 2015 survey of growers in 11 states found feral swine caused nearly $200 million in crop damage annually in corn, soybeans, wheat, rice, peanuts and sorghum. Actual damage is much higher because the wild pigs aren’t just found in those states and crops.

 “Feral swine damage everything,” said Stephanie Shwiff, a research economist at the center, recalling a meeting where every farmer present reported losses from wild pigs. “The one kind of grower people thought wouldn’t have a problem were the tobacco farmers, but even they have crop losses from the pigs rooting in their fields.”

Shwiff’s job is to go beyond the basic statistics  gathered by the wildlife services – this many predators or pests killed and that many head of cattle or sheep saved – to report the impacts of those actions.

“What are the benefits of damage management? What are we getting for our investment?” she said. “We look at  damage and damage mitigation in the broader economic context. If you save 1,000 head of sheep or 5,000 acreas of corn, how does that impact the regional economy and jobs?”

For feral swine, you can also ask the question in reverse.

“If we remove 50 percent of the wild pigs, how does that affect the harvest of crops, or the profitability of livestock?” Snow said. “For us, the removal of pigs is great, but it’s not the best metric of success.”

Those specific answers aren’t known for feral swine yet, but others are. Management efforts, for instance, must reduce pig populations by 70 percent each year to keep them from growing. Ground and aerial shooting and trapping are the current methods being used to manage swine populations, but Snow and others are also working on a new kind of toxic bait.

And ironically, it’s made from sodium nitrite, the food preservative commonly found in bacon and sausage.

Testing the New Bait

“It’s a new active ingredient that’s not registered yet for use in the United States, although it is in New Zealand where they also have a feral swine problem,” Snow said. “And it has some upsides and downsides.”

The positives of the new toxic chemical are that it’s fast-acting, very effective, appears humane and doesn’t present nearly the risk of secondary exposure that blood-thinning poisons do.

“It works by preventing oxygen from attaching to red blood cells,” Snow explained. “So it mimics carbon monoxide poisoning. The pigs get woozy, then fall unconscious and die within two or three hours.”

The meat of swine killed in this manner isn’t poisonous, so the risks to other wildlife – or hunters who may shoot a pig in that small window before it dies – aren’t high. But they aren’t zero, either, and Snow and his colleagues are considering those risks now and how they might be mitigated.

The downside of sodium nitrite as a toxic bait is that it tastes really, really bad.

“It’s taken a lot of work to get it in a bait that pigs will eat,” Snow said. “It’s been hard – pigs are smart.”

Not only does the bait have to be attractive to swine, it shouldn’t be too attractive to deer, raccoons and other wildlife. The current formulation hides the foul-tasting toxin in a peanut-based bait, but it’s using swine-specific bait stations that makes it effective against pigs while protecting non-target species.

“The way you get pigs to come in and eat the toxic bait is to pre-bait them for 10 to 14 days,” Snow explained. “You train them to use a bait station. The bait station is designed to take advantage of the pigs’ feeding behavior and many pigs can access the bait at once.”

It sounds burdensome, but baiting can be more effective than shooting and trapping because, again, pigs are smart. They get scared away by shooting and learn to avoid traps. The pre-baiting, with tasty food, gets the pigs trained to come to the bait station, come in numbers and come hungry.

“Then when you switch to the toxic bait, they eat enough to get a toxic dose,” Snow said. “It leads to whole sounders of pigs being removed from an area at once.”

 And that gives a whole new meaning to the term “pig out.”


For More Information

Distribution map 

Disease risk

Resources and outreach material