Feral hogs are one of the earliest and most successful invasive species to invade North America. European settlers brought domesticated hogs over on ships and released them in the wild for a familiar food supply. However, in the short time the feral hogs have been present, they have outcompeted native species for resources and pushed them to the brink of extinction, all the while causing millions of dollars in damage every year.
The feral hog (Sus scrofa) is a highly social, intelligent animal that can weigh more than 300 pounds, larger if the hog recently escaped from being domesticated. S. scrofa are nocturnal and have an omnivorous scavenger diet that includes berries, carrion and trash. Their tusks are used as tools, weapons for self-defense, and competing for a mate. Sows can have litters that range from 4-6 piglets and can have two breeding seasons per year. The hogs historical range stretched from the east coast of Asia to the west coast of Europe, and even reached as far south as northern Africa, where their natural predators included wolves and tigers.
Nowadays, when domestic pigs escape, they can become feral fairly easily. Once the domesticated hogs escape and become feral, they quickly join the feral hog population and damage trees, vegetation, agricultural crops, feed on the eggs of ground-nesting birds and turtles, and can carry disease (Masterson, 2007). All of these activities alter the energy flow and nutrient cycling from ecosystems and their native species. Rooting is a mechanism that hogs use to turn up soil looking for food. Acorns and other nuts are valuable food source for wild pigs (West et al. 2009). However, rooting accelerates decomposition of leaf litter, resulting in a loss of nutrients from the forest floor (Singer et al. 1984). This activity stresses established trees, such as oak trees, while destroying the seedlings that were not already consumed as acorns.
These acorns and other hard mast that are consumed by the hogs, are a vital food source during the fall for other native species, such as the White-Tailed Deer. Feral hogs directly compete with the deer, however, deer tend to stay away from hogs which means they may have to stay away from the best feeding grounds. Feral hogs are also known to carry disease that can be spread to other wildlife, livestock, and some times but rarely humans. Some diseases of feral hogs include pseudorabies, swine brucellosis, tuberculosis, bubonic plague, tularemia (Taylor, 2003). These are new diseases for many newly invaded ecosystems so many native species have no immunity towards them, which further strengthens the competitive advantage hogs have over native wildlife.
This creates a positive feedback loop that is further complicated by the high breeding rates and large litter sizes that feral hogs have. Sows have up to 10 offspring per litter, and are capable of having two litters per year. Piglets reach sexual maturity around 6 months of age, and this is compounded by the fact of not having any natural predators (Perot, 2011).
Feral hogs have many indirect effects on ecosystems, as well. Threatened subspecies of Black Bear, that have been eradicated from most of Texas and Louisiana are starting to make a comeback and return to their former range. However, feral hogs, which are significant pests for many farmers and ranchers, closely resemble the black bear, so in trying to control the feral pigs, they are sometimes shooting the bears, which happened to Gary Kinsland in 2010 (“Lessons Learned”, 2010). Also, the hogs are lowering biodiversity by driving native species towards extinction, and simplifying the ecosystem so much, that it could lead to more frequent and intense disturbances.
Despite that, it is possible for feral hogs to help against other invasive species. Burmese Pythons have become an ecological disaster in the Florida Everglades. Many wildlife species are being pushed toward the brink of extinction, with no answers in sight. At the same time, feral hogs are abundant in most of Florida, reaching much of the Everglades. Both the hog and the python evolved together in Asia, before being transported to the Americas. The hogs high breeding success in the United States, could potentially act as a buffer, which could allow enough time for many native species to acclimate and possibly begin to adapt to the new invaders.. The potential benefits of invasive species are usually decided by social issues and the values of our society.
Most invasive species have a negative connotation in our society. However, usually that reputation is quite accurate and feral hogs are no exception. One estimate of feral hog damage to agriculture and the environment in the United States is $1.5 billion annually (Pimentel 2007). Most of this damage is done through consuming or trampling the crops. Ranchers have to constantly tend to their fences for the livestock, because hogs will upend the fences allowing livestock to escape or be consumed by the hogs themselves (West et al. 2009).
Not all consequences of the feral hog being present are negative. Feral hogs give plenty of hunting opportunities and seem to be able to keep pace with a heavy amount of hunting pressure. Most states allow for year long hunting season for feral hogs, and some states like the Missouri Department of Conservation requests that hunters who encounter the hogs shoot them on sight (“Shoot on Sight”, 2012). Feral hog populations also gives job opportunities to many states that spend money trying to control their numbers. Many states even set up helicopter hunts that allow civilians and extreme hunters the opportunity to hunt hogs from a helicopter.
The majority of the management techniques used for feral hogs has only had moderate success at best. Hog populations continue to explode and are now beginning to spread over the rest of the United States. While humans are one of the most successful species at pushing other species to extinction, it seems that feral hogs are making themselves an exception to the rule, by adapting to us faster than we can hunt them. One control method that could have some success is try to create a market for feral hog meat. While they do have higher rates of disease than livestock, if harvested correctly and cooked thoroughly the meat is perfectly safe. Feral Hogs have a lower fat ratio than domesticated pigs due to wider diet and much more exercise. Regardless, as our knowledge grows about the behavior of feral hogs and other invasive species, we will change management techniques to more successful practices.
“Frequently Asked Questions-Wild Pigs « Coping with Feral Hogs.” Coping with Feral Hogs. Web. 03 Feb. 2012.
“Lesson Learned: Hog or Bear? Know Your Target.” Louisiana Department of Wildlife and Fisheries. Web. 03 Feb. 2012.
Masterson, J. (12 June 2007). “Sus scrofa”. Smithsonian Marine Station at Fort Pierce. Retrieved 3 February 2012.
Perot, Michael. “Coping with Feral Hogs.” Coping with Feral Hogs . Louisiana Forest Stewardship Program, 2011. Web. 3 Feb. 2012.
Pimentel, D. 2007. Environmental and economic costs of vertebrate species invasions into the United States. Pages – 8 in G. W. Witmer, W. C. Pitt, and K. A. Fagerstone, editors. Managing vertebrate invasive species: Proceedings of an international symposium. USDA APHIS Wildlife Services, National Wildlife Research Center, Fort Collins, Colorado, USA.
Singer, F. J., W. T. Swank, and E. E. C. Clebsch. 1984. Effects of wild pig rooting in a deciduous forest. Journal of Wildlife Management. 48:464– 473.
West, B. C., A. L. Cooper, and J. B. Armstrong. 2009. Managing wild pigs: A technical guide. Human- Wildlife Interactions Monograph 1:1–55.