The three (million) little pigs: why the United States must do more than huff and puff.

• Author: Lefkowitz, Dian
• Position: Wild pigs as introduced species

1. INTRODUCTION

   It reads like a war novel. A strange and foreign being has landed on U.S. soil, bent on destroying everything in her path. One moment she is a distant figure in the dark; the next, you can hear the wind glance off her fangs. Some 300 pounds of sinew and bristle, nerve and hunger, she is the greatest ecological threat stalking the American wild. She is a keen hybrid: feral yet adaptive, vicious yet intelligent, aggressive and spreading like fire. She is the wild pig.

   The United States is no stranger to non-native invasive species. (1) Through legislation and Executive Orders, the country has managed to mitigate the damage wrought by plants and animals that threaten the ecosystem and pose dangers to humans. (2) However, the bulk of effective national legislation has focused on aquatic life forms whose main threats, while serious, lie in their disruption of infrastructure and pollution of the environment. (3) Never before has a Federal statute been constructed that could reign in the havoc wreaked by the most prolific large mammal in the American landscape. (4) If the nation is to have any hope of reclaiming its land from the jowls of this savage hunter, it will have to follow the lead of Australia, a nation that has managed, through legislation, to fence in the devastation caused by this cunning beast. (5) Section

   II of this note will present the wild pig as a species, detailing its introduction to North America, the scope of damage it leaves in its wake, and current management tactics in both the U.S. and Australia. (6) Section III will present the history of U.S. legislation aimed at managing invasive species, both in general and in this specific case, and will outline Australia's legislative history addressing like management. (7) Section IV will analyze the results and explain the benefits of adapting Australian measures on U.S. soil. (8)

2. Facts

   1. Sus Scrofa: The Wild Pig

      1. Introduction to the Continental United States

         North America's only native wild pig is the collared peccary, Tayassu tajacu. (9) The first domestic hogs in the Americas were introduced by European explorers in the 16th century; the release of these hogs' descendants forms the earliest source of wild pig populations in the Continental U.S. (10) Aside from these early releases, however, the vast majority of wild pig entrances is due to open range practices by farmers and settlers, continuing into the mid-1900's. (11) The establishment of Eurasian wild boar populations likely resulted from importation into North Carolina from Germany in the early 20th century. (12) The variety of wild pigs in the United States today, referred to taxonomically as Sus Scrofa, represents the interbreeding of these Eurasian wild boars and the feral descendants of the early explorers' hogs. (13)

      2. Nomenclature and Identification

         Within the genus Sus, sixteen or seventeen species have been identified, roughly falling into four categories. (14) Sus Scrofa, truly a composite of several disparate lines, varies widely in appearance. (15) Male wild pigs possess continually growing upper and lower canine teeth, or tusks, which grow upward and sharpen due to friction; lower tusks can grow to be an average of 185mm. (16) Males typically compete aggressively over food and breeding, leading to tusk scars on adult male bodies. (17)

         Average physical dimensions vary once again, although typical weights for adults range from seventy-five to 250 pounds, with lengths ranging from fifty to seventy-five inches. (18) Individual wild pigs can grow much larger, beyond 800 pounds in some cases. (19) Many outlier weights result from the intentional feeding of captive pigs which are later illegally released into the wild. (20)

   2. Damage

1. Economy

   Attempting to pinpoint national figures on damage poses problems that serve as a microcosm for the larger issue surrounding the wild pig's management: numbers appear to exist solely on a state-by-state basis and they increase too rapidly for documentation--even under the purview of the United States Department of Agriculture (USDA), studies and presentations tend to reflect individual states' research and concerns. (21)

   A primary obstacle to damage valuation is the lack of established means of applying monetary values to land units, particularly where studied land likely varies in usage. (22) Further complicating these efforts are so-called "spillover" effects, also known as secondary multiplier effects. (23) Considering the myriad, integrated ways in which economic damage is sustained by the presence of wild pigs, understandably it is, basically impossible to accurately appraise the national loss in a dollar amount. (24)

   2. Ecology

      Wild pigs wreak havoc on their habitats. (25) A study of wild pigs in the Great Smokey Mountains National Park reports that the destructive foraging exposed several thousand tree roots per hectare, reduced plants cover by as much as 80%, and increased bare ground by nearly 90%. (26) Forest litter and soil bulk density were also greatly reduced while erosion and nutrient loss from the forest floor to receiving river waters were doubled. (27) The resulting damage was the widespread loss of native vegetation, which caused the spread of opportunistic weeds into newly disturbed areas. (28)

   3. Disease

      Wild pigs represent a highly mobile source of serious disease. (29) They carry pseudorabies (Aujeszky's disease, porcine herpesvirus 1), a viral swine disease that has a significant economic impact on the commercial hog industry. (30) As secondary hosts, cattle are especially prone to infection, which lead to diseases, such as mad itch. (31) Other known secondary sources include "rats, dogs, and horses." (32)

      In addition, wild pigs are "a source of trichinosis and of swine brucellosis, which is potentially fatal in humans." (33) In 2006, an outbreak of spinach-related E. coli contamination resulted in three human deaths and over 200 illnesses; the path of the infection suggests that wild pigs transported the pathogenic E. coli strain from nearby cattle pastures to the spinach fields. (34)

      3. Pigs vs. Humans

   1. Highly Adaptive Traits

      The Southeastern Cooperative Wildlife Disease Study, which has tracked wild pig populations since the early 1980's, has noted their steady spread into new areas; wild pigs exist in at least 39 states today. (35) Although it was once believed that wild pigs strongly favored warm climates and would be unable to expand into colder areas, current mapping suggests that wild pigs can tolerate climates ranging from the hot deserts of Mexico to the harsh freezing temperatures of Michigan and North Dakota. (36)

      Ecologists classify wild pigs as a generalist species, meaning they readily adapt to a variety of habitat types and environmental conditions. (37) Wild pigs have adaptive diets that while consisting of a high percentage of plant matter and invertebrate animals, such as worms and insects, also include small mammals, young large mammals, and even reptile and bird eggs. (38)

      Furthermore, compared to other mammals of similar size, wild pigs have a high reproductive potential, making them one of the most prolific large mammals on the planet today. (39) Although young pigs are vulnerable to predators such as eagles, hawks, owls, foxes and bobcats, once a pig reaches about forty pounds, they are generally safe from nonhuman predators. (40) As a result of their natural adaptability and reproductive proliferation, wild pigs in the United States make accurate population censuses nearly impossible. (41) Despite the difficulties in mapping and assessing the spread and density of the pig, evidence from multiple studies and efforts suggest that wild pigs densely populate many regions and are expanding their range into previously unoccupied areas. (42)

   2. Current Management and Lethal Control Tactics (43)

      Population dynamics are a key factor in designing and implementing control strategies. (44) Environmental conditions have a great deal of influence on the reproductive capacity of wild female pigs that in particular areas with limited food availability, juvenile females generally do not breed. (45) Therefore, in certain areas, recreational hunting that removes mostly adults may be a successful tactic on its own. (46)

      In areas with plentiful food sources, however, juvenile breeding can contribute nearly as much to population growth as can adults. (47) Furthermore, supplemental feeding sources, such as agricultural crops or feed meant for livestock, can bolster populations thereby making reduction implausible. (48) Therefore, in order to be effective, population control strategies must use a combination of tactics, which are implemented aggressively and include continuous monitoring by ongoing population surveys. (49)

      Trapping, followed by euthanasia, as opposed to release, is the most important distinct tool in depopulation efforts. (50) In general, cage traps, especially side- or top-hinged, are popular for being both lightweight enough to set up, and strong enough to prevent escape. (51) Problems with trapping include the accidental capture of deer and other wildlife; furthermore, pigs can smell human presence and may veer away from the scent if humans or dogs have been present. (52)

      Proper trap design is essential and is often referred to by trappers as an "art" form in itself because if not done properly, in rectangular traps especially, pigs are known to "congregate in corners" and escape by climbing on each others' backs, even over walls as high as six feet. (53) For this reason, many trappers install wire tops to the cages, however, this can cause unwanted mortality when other untargeted species, such as deer and bears, become trapped. (54) To combat this dilemma, some advocate for the use of circular traps; still, "while it is possible to keep the population in check with continuous control, [trapping] is highly unlikely to eradicate a hog population within an established...