Invasive Species: Wild Boar

Feral hogs can destroy crops, alter entire ecosystems and affect native species.

Dominant wild boar
JMrocek / Getty Images

Wild boars are an invasive type of pig that are largely distributed around the world. They go by many names, including wild hog, razorback, piney woods rooter, feral hog, and feral pig. Technically, these animals are of the same species as pigs found on farms, and most populations are believed to be descendants of domesticated pigs who have either escaped or been released.

In general, wild boar are differentiated from domestic pigs by their thinner bodies, thicker hides, longer tusks, and coarse, bristly hair, though the biggest difference comes by way of their knack for destruction. Wild boar routinely cause extensive damage to both private property and agricultural land through tree rubbing and digging (known as "rooting") as they search for food, but their presence can also alter ecosystems and affect native species. Countries other than the United States with large populations of wild boar are also susceptible to African swine fever, a deadly disease with no cure or vaccine that can spread rapidly from wild pigs to domesticated ones.

According to the United States Department of Agriculture (USDA), feral swine are responsible for well over $1.5 billion worth of damage in the United States each year. In 2018, however, CNBC reported that the number may be closer to $2 billion or even $2.5 billion, with damages to agriculture alone costing about $1 billion annually. Dale Nolte, the USDA’s national feral swine program manager at the time, told the network that wild boar were capable of damage in almost all sectors due to their intelligence and adaptability.

Wild Boar Facts

  • Size: Wild boar are usually smaller than domestic pigs. Adults will average anywhere from 75 to 250 pounds in weight—though there have been accounts of certain individuals growing to be much larger.
  • Reproduction: They breed year-round with litters of four to 12 piglets each year. Feral piglets are striped or spotted but can vary in colors and patterns (from white and black to brown and red) once they mature.
  • Social Groups: Females, called sows, often band together to form family groups of up to 30 members, while males live alone or in small groups of other males.
  • Geography: In the U.S., the largest populations of wild boar live in the South, particularly in Texas.
  • Activity: Wild boar can run at speeds up to 30 miles per hour and are more often active at night. They are also considered much stronger than domestic pigs.

How Did Wild Boar Become a Problem in the United States?

Wild hogs were first brought over to the United States by early explorers and settlers as a food source in the 1500s. Eventually, enough pigs escaped from their enclosures to form individual populations which spread into other parts of the country. In the 1900s, Eurasian wild boar were brought over from Russia for sports hunting and hybridized with the original wild species. According to USDA estimates, the current population of wild boar in the United States exceeds 6 million animals, and they are present in at least 35 states including Hawaii.

Feral hogs are able to adapt to a wide range of environmental conditions and have few natural predators outside of wolves, an ideal scenario for them to become an invasive species. Plus, the size of a wild boar’s home range can vary between 0.23 square miles and 18.64 square miles, so populations are rapidly expanding and spreading all the time.

Problems Caused by the Wild Boars

Traces of wild boar on a forest road
Wild boars damage plants through digging and rooting. Piotr Wytrazek / Getty Images

Most of the environmental issues caused by wild boar in the U.S. occur in the Southern states. In Texas, where feral hogs are responsible for $50 million worth of crop damage each year, the government has opened up hunting via helicopters and even hot air balloons in an attempt to curb populations.

A report by the Texas Parks & Wildlife Department calculated that the wild pig population in the United States increased from 2.4 million to 6.9 million between 1982 to 2016, with 2.6 million living in Texas alone. They’re able to disturb the environment on a large scale, which affects the ecosystems and critical habitats of a wide range of native species:

“They use their snouts to dig into the ground and turn over soil in search of food resources, altering the normal chemistry associated with nutrient cycling within the soil. Further, the mixing of soil horizons that often accompanies rooting by wild pigs has also been shown to alter vegetative communities, allowing for the establishment and spread of invasive plant species. It has been estimated that a single wild pig can significantly disturb approximately 6.5 ft2 in just one minute.”

Wild boar will eat almost any crop available to them, including valuable ones like corn, soybeans, wheat, and rice, as well as fruits and vegetables. Most damage from wild boar comes from uprooting or devouring crops, but they’ve also been known to contaminate water sources or contribute to mosquito-borne disease as they wallow in mud to maintain body temperature. Both rooting and wallowing can also increase erosion or decrease soil quality, and even alter the understory growth of forests and decrease the number of trees. After wallowing, wild boar tend to rub themselves on plants to shake off pests, resulting in destroyed shrubs or trees.

Although African swine fever hasn’t been an issue in the United States, wild boars are capable of other cross-species disease transmissions between wildlife, domestic animals, and humans alike. A 2017 study investigated 84 different wild pig pathogens and found that 87% could be transmitted to other species, especially among cattle, sheep, and goats. The researchers also found that at least 40% of reportable domestic animal diseases in North American are zoonotic (meaning they are caused by a pathogen that has jumped from an animal to a human).

According to a 2018 study, wild boar are considered threats to 87% of the species they share habitats with in the contiguous United States. They don’t just cause problems by damaging plants, they also threaten native species by destroying habitats, transmitting disease, and as predators. They can compete with native species like bear and deer for food, habitats, or water, disrupting the overall balance of the food chain or deteriorating the food source of an entire wildlife population.

Depending on the region, wild boar can also endanger certain species of nesting birds and reptiles as they prey directly on eggs or actively hunt. On the west coast of Australia, for example, they account for 89.6% of deaths among threatened marine turtle nest eggs.

Efforts to Curb Environmental Damage

Wild boar piglets
Wild boar piglets are usually striped or spotted. Bernard Stam / EyeEm / Getty Images

Non-lethal techniques to manage wild boar include installing fencing or vaccinating livestock against diseases, but most of the current widely used options involve hunting and trapping. Wild boar are also considered highly intelligent, so questions of ethics and animal welfare have inspired scientists to come up with options outside of culling.

Research on contraceptives as a tool to reduce populations of wild boar was conducted in Finland in 2019, but the study found that most of the viable pig vaccines available had to be administered intramuscularly (the pig would have to be caught and handled first). Since wild boar are so widespread and numerous, administering enough contraceptives to make a difference would prove difficult. What’s more, delivering a vaccine through a dart remotely may drive the feral pig population further into more regions as they escape human chasing. The best solution, they suggest, would be to develop an oral contraceptive for wild boar and administer it through baits, though more research is needed.

Another argument for finding alternative management methods is that wild boar are expensive to remove. In 2011, when local governments organized a management program to eliminate a new population of wild pigs who’d established themselves in Illinois, the cost to remove each pig averaged $50 per animal. For the first 99% of the pigs, it took about 6.8 hours of effort per pig between camera trapping and baiting, but costs increased 84-fold once they reached the remaining 1%.

The idea of eating invasive wild boar is always on the table, but allowing the sale of wild pigs as a food source has its own set of obstacles. Wild boar may put humans in danger of diseases like brucellosis, although an experienced hunter can practice safe techniques to significantly lower the risk of exposure. There’s also the fact that many farmers see wild boar as a massive nuisance, and a management technique in one region may not be suitable for another. In Tennessee, for example, relocation and allowing for sale are the two least accepted and most controversial options for wild boar management among rural landowners.

The federal government has employed several programs in response to the environmental and economic consequences of wild boars. Most recently, the Feral Swine Eradication and Control Pilot Program established by the 2018 Farm Bill received $75 million in funding. Initially, over $16.7 million were allocated to 20 feral swine pilot projects in Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, Oklahoma, North Carolina, South Carolina, and Texas. The second round of funding began in January 2021, consisting of $11.65 million spread out among 14 two-year projects helping farmers and landowners control wild boar in Alabama, Hawaii, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, and Texas. Projects include the capture and removal of the animals as well as restoration of ecosystems already affected by wild boar.