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Feral Pigs

True wild pigs are not native to the United States. Only the collared peccary that inhabits the southwestern and south-central parts of the United States is native. Feral swine (Sus scrofa) in the United States have originated from varieties of domestic swine, Eurasian wild boar, and their hybrids. Domestic swine were introduced to the United States as early as 750-1000 A.D. in Hawaii. In the 1500s, Spanish explorers such as DeSoto and Cortez were the first to bring domestic swine to the United States mainland. By the 1960s, they were established in more than 20 states (McKnight 1964). Swine introductions have intentionally or accidentally occurred by a variety of means. Swine have been transported and let loose to establish populations for hunting. Some have escaped from shooting preserves or confinement operations. Domestic swine have avoided capture in free-ranging livestock operations or been abandoned by their owners. Feral populations have dispersed (Gipson et al. 1997, Witmer et al. 2004).

Damage

Feral swine are the most abundant free-ranging exotic ungulate (hooved animals) in the United States (McKnight 1964, Decker 1978) and have become widespread because of their reproductive potential and adaptability to a wide range of habitats. An estimated population of 4 million feral swine currently occur in the United States (Pimentel et al. 2000) with the largest populations inhabiting Texas, Florida, Hawaii, and California.

Feral swine eat both plant and animal matter. The majority of their diet consists of plant shoots, roots, tubers, fruit, and seeds and nuts such as acorns and hickory nuts. Common agricultural crops affected include hay, small grains (milo, rice, and wheat), corn, peanuts, vegetables, watermelons, soybeans, cotton, orchards, horticultural crops, and conifer seedlings. Additionally, swine rooting and digging for food with their snouts, loosen the soil and accelerate erosion, setting back plant succession, reducing earthworm activity, and contributing to exotic plant invasion (Mungall 2001).

As a predator, feral swine eat salamanders, frogs, fish, crabs, snakes, turtles, rodents, muskrats, eggs and chicks of ground-nesting birds, white-tailed deer fawns, and livestock. In Florida, feral swine have contributed to the decline of at least 22 plant species and 4 species of amphibians listed as rare, threatened, endangered, or of special concern (USDA 2002). In the southern United States, feral swine predation may negatively affect bobwhite quail and wild turkey nest success. On some southeastern United States beaches, feral swine have become significant predators of threatened and endangered marine turtles (loggerhead, green, leatherback, hawksbill, and Kemp's ridley) feeding on the eggs (USDA 2002).

Diseases

Feral swine can harbor numerous viral and bacteriological diseases. The diseases of most concern to the livestock industry include pseudorabies, swine brucellosis, bovine tuberculosis, leptospirosis, and vesicular stomatitis (Becker et al. 1978, Williams and Barker 2001). These and the possibility of an exotic disease outbreak such as foot-and-mouth disease, a contagious viral disease of ungulates (e.g., pigs, sheep, cattle, goats, and deer) (Pech and McIlroy 1990), or classic swine fever (a contagious viral disease of wild and domestic swine), could have serious repercussions for livestock industries (Hone et al. 1992).

Population Control and Management

In most states feral swine are unprotected or classified as an agricultural pest, therefore hunting methods are liberal and swine can be harvested throughout the year. States where feral swine are classified as game animals rely on hunter harvest to control or regulate swine populations. Frightening devices are ineffective and no repellents or toxicants are registered for feral swine use in the United States. Other lethal means for eradication include aerial hunting with helicopters, hunting with dogs, or shooting at night over bait. Other control measures to alleviate damage include excluding feral swine with wire mesh fencing or electric fence. No fence design is completely pig-proof, but they can significantly reduce feral swine movement into protected areas.

Summary above taken from:

SEWARD, N. W., K. C. VERCAUTEREN, G. W. WITMER, AND R. M. ENGEMAN. 2004. Feral swine impacts on agriculture and the environment. Sheep & Goat Research Journal 19:34-40.

Literature Cited

BECKER, H. N., R. C. BELDEN, T. BREVAULT, M. J. BURRIDGE, W. B. FRANKENBERGER, AND P. NICOLETTI. 1978. Brucellosis in feral swine in Florida. Journal of the American Veterinary Medical Association 173: 1181-1182.

DECKER, E. 1978. Exotics. Pages 249-256 in J. L. Schmidt and D. L. Gilbert, editors. Big game of North America: Ecology and management. Stackpole Books, Harrisburg, Pennsylvania, USA.

GIPSON, P. S., B. HLAVACHICK, T. BERGER, AND C. D. LEE 1997. Explanations for recent range expansions by wild hogs into midwestern states. Great Plains Wildlife Damage Control Workshop 13: 148-150.

HONE, J., R. PECH, AND P. YIP. 1992. Estimation of the dynamics and rate of transmission of classical swine fever (hog cholera) in wild pigs. Epidemiology and Infection 108: 377-386.

MCKNIGHT, T. 1964. Feral Livestock in Anglo-America. University of California Publisher of Geogeology Number 16. Berkley, CA, USA.

MUNGALL, E. C. 2001. Exotics. Pages 736-764 in S. Demarais and P. R. Krausman, editors. Ecology and management of large mammals in North America. Prentice Hall, Upper Saddle River, New Jersey, USA.

PECH, R. P., AND J. C. MCILROY. 1990. A model of the velocity of advance of foot-and-mouth disease in feral pigs. Journal of Applied Ecology 27: 635-650.

PIMENTEL, D., S. MCNAIR, J. JANECKA, J. WIGHTMAN, C. SIMMONDS, C. O'CONNELL, E. WONG, L. RUSSEL, J. ZERN, T. AQUINO, AND T. TSOMONDO. 2000. Economic and environmental threats of alien plant, animal, and microbe invasions. Agriculture Ecosystems and Environment 84: 1-20.

USDA. 2002. Environmental assessment: Management of predation losses to state and federally endangered, threatened, and species of special concern; and feral hog management to protect other state and federally endangered, threatened, and species of special concern, and candidate species of fauna and flora in the state of Florida. United States Department of Agriculture, Animal Plant and Health Inspection Service, Wildlife Services, Gainesville, FL, USA.

WILLIAMS, E. S., AND I. K. BARKER. 2001. Infectious diseases of wild mammals. Iowa State University Press, Ames, Iowa, USA.

WITMER, G. W., R. B. SANDERS, AND A. C. TAFT. 2003. Feral swine--are they a disease threat to livestock in the United States? Proceedings of the Wildlife Damage Management Conference 10:316-325.