What do Pueraria montana (a.k.a. kudzu), Myocastor coypus (a.k.a. nutria) and feral versions of Sus scrofa (a.k.a. feral hogs) have in common? Although these species are distinctly different, they share a dubious similarity. Each represents a destructive invasive species brought to or expanded in this country under beneficial pretenses. Kudzu, that aggressive vine which overtakes roadsides and smothers native vegetation, hails from East Asia. It was first brought to the U.S. in the late 1800’s and later promoted as an erosion control and forage plant during the Great Depression era. The nutria, a semi-aquatic, herbivorous rodent is native to South America. It was brought here in the 1930’s to establish nutria fur ranches. The fur farms are now defunct, but expanding populations of nutria are wreaking havoc on native vegetation in the marshlands of Louisiana and Maryland. Feral hogs are free roaming, semi-wild versions of domestic commercial swine or its ancestral cousin, the Eurasian wild boar released for hunting purposes. In many cases they are viewed as an interesting novelty and a game animal for sport hunting. But the spread of feral hogs in Virginia and other states is no amusing matter. They are listed as an invasive species by USDA for good reasons. Farmers, rural landowners, and hunters definitely should not condone importation of feral hogs into the Commonwealth and in fact should take active steps to prevent expansion of feral hogs in the state.
How Many and Where?
Unfortunately the U.S. feral hog population is well established and growing. Precise determination of any wildlife population is impossible, but recent estimates indicate approximately 4 million feral hogs exist in the U.S. By comparison the September 2010 USDA inventory of hogs and pigs raised for agricultural purposes (i.e. on hog farms) was 65 million. Texas has the largest population of feral hogs estimated at 1 to 1.5 million followed by Florida with as many as 500,000, Hawaii with as many as 80,000 and California with as many as 70,000 (reviewed by Seward and co-workers, 2004). More recent information indicates that the population is growing and spreading. Feral hogs are now reported in 39 states (Southeastern Cooperative Wildlife Disease Study, 2009; http://www.scwds.org/).
Virginia is one of these 39 states. A well known population of feral hogs has existed in the Back Bay National Wildlife Refuge near Virginia Beach for many years. The relatively isolated and confined location at Back Bay has allowed this modest population to be effectively managed and contained. But feral hogs and hog groups have been increasing in areas more difficult to manage including the western Appalachian, central Piedmont and Eastern regions, with reports of feral hogs in at least 21 Virginia localities (see Figure; Gray and Wilhelm, 2010). The total population is unknown but is certainly less than populations in the lower southeastern states. However, the potential is real for feral hog populations in Virginia to grow by natural range expansion and by illegal or ill advised translocation.
What Is the Problem?
Feral hogs are adaptive and prolific. As opportunistic omnivores they satisfy their nutritional needs from a variety of plant and animal food sources. Early sexual maturity, production of offspring in litters, and absence of natural predators creates the potential for feral hog populations to grow rapidly where habitat conditions are good. These natural advantages are precisely what have allowed feral hogs to become the invasive, problem causing species that they are (reviewed by West and co-authors, 2009).
From an ecological standpoint, feral hogs damage natural land features and native plants.
Rooting, feeding, tramping, denuding and soil compaction can all have a disruptive influence in woodlots, streambeds, natural clearings and native plants. Feral hogs compete with native wildlife species for oak and other mast food sources. In addition they may feed on frogs, salamanders and other small animals. When the opportunity is presented, feral hogs will feed on eggs of ground nesting birds such as wild turkey and quail.
Similar damage occurs in agricultural situations. Feral hogs will root, trample and compact pasture, hay and crop fields and will actively feed on the existing crop. One legitimate source has estimated U.S. agricultural and environmental damage losses from feral hogs to be valued at $1.5 billion annually (reviewed by West and co-authors, 2009).
Commercial swine production is important to Virginia’s agricultural economy and many other states as well. A major concern with the development of feral pig populations is the fact that they may serve as reservoirs for several economically important swine diseases. Swine brucellosis and pseudorabies are two diseases that have been previously identified in isolated blood sampling of captive feral hogs in Virginia. Both of these diseases have significant potential to cause serious losses on individual hog farms or within a geographic region. Currently Virginia holds brucellosis and pseudorabies free status in its domestic swine herd, and it is important for animal health and economic reasons to maintain this status. Classical swine fever (formerly called hog cholera) and toxoplasmosis are additional diseases for which feral hogs can serve as a reservoir and a vector.
What Should the Strategy Be?
First and foremost it is not wise for landowners or hunters to bring in or translocate feral hogs for hunting or other purposes. Indeed feral or wild hogs are classified as nuisance animals in Virginia and it is illegal to release hogs to the wild. Considering that our state is blessed with many native game species and that feral hogs can be detrimental to native species and their habitat, it is simply bad policy to add feral hogs to the system.
For existing populations, hunting and shooting can reduce numbers in isolated situations. The Virginia Department of Game and Inland Fisheries encourages harvest of as many of these animals as possible. To hunt feral hogs, a hunter must have a hunting license and landowner permission. There is no closed season or daily bag limit on feral hogs, although hunting is not lawful on Sunday. However, past experience and research has shown that in regions of good habitat for feral hogs, traditional hunting alone is unlikely to eliminate them from an area.
In states with severe problems such as Texas and Florida, combinations of traditional hunting, trapping followed by euthanasia and even aerial shooting from helicopters and night shooting have been employed to get populations under control. Hopefully the problem does not reach this magnitude in Virginia, but the potential exists for significant feral hog expansion. Hunters, landowners and farmers who sight feral hogs should alert appropriate local professionals such as agricultural Extension Agents or Game Wardens. Currently the Wildlife Services Division of USDA-Animal and Plant Health Inspection Service based in Moseley, Virginia conducts a blood testing program to monitor the state’s feral hog population for swine brucellosis, classical swine fever and pseudorabies. Local officials may report potential new sub-populations to this agency for inclusion in the monitoring program. Ultimately problem cases may require coordinated efforts among landowners, USDA-APHIS Wildlife Services, Virginia Department of Game and Inland Fisheries and the Office of the State Veterinarian.
Seward, N.W., K.C. VerCautern, G.W. Witmer, and R.M. Engeman. 2004. Feral swine impacts on agriculture and the environment. Sheep and Goat Research Journal. 19:34-40.
Southeastern Cooperative Wildlife Disease Study (SCWDS), College of Veterinary Medicine, University of Georgia, Athens, GA; http://www.scwds.org/ (accessed Dec. 20, 2010).
West, B.C., A.L. Cooper, and J.B. Armstrong. 2009. Managing wild pigs: a technical guide. Human-Wildlife Interactions Monograph 1:1-55 (The Berryman Inst., Starkville, MS).
Virginia Cooperative Extension materials are available for public use, re-print, or citation without further permission, provided the use includes credit to the author and to Virginia Cooperative Extension, Virginia Tech, and Virginia State University.
Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Alan L. Grant, Dean, College of Agriculture and Life Sciences; Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Jewel E. Hairston, Administrator, 1890 Extension Program, Virginia State, Petersburg.
January 1, 2011