Wild pigs are a very good example of the complexities of the Invasive Species problem. Pigs are not native to the United States but have exploded in population and become a major problem. In Italy meanwhile, the population of native wild pigs has also exploded.
In both Italy and Texas human behavior and activity are at the root of the problems.
Pigs (Sus Scrofa) were aboard ship with Columbus when he landed in the
West Indies in 1493. They reached Florida with Hernando de Soto in 1539. The animals have been aboard ship with humans for millennia. This is because, as Texas says, they are “a sustainable low-maintenance source of food.” The release or escape of these invaders was the beginning, but not the end of the problem. It got worse.
As Texas Parks and Wildlife says (citations refer to information on website):
“As explorers moved across the continent those domestic pigs would often be left behind, establishing the first populations of feral pigs in North America (5). The term feral refers to a domestic animal that has gone wild. Following these initial introductions, European settlers and Native Americans implemented free-ranging farming practices of domestic pigs that promoted the spread of feral pig populations (1, 6).”
” Free-range farming methods were still practiced in some states through the 1950s (1). In addition to these feral pigs, Eurasian wild boar have been imported and released as an exotic game species for recreational hunting purposes across the United States since the early 1900s (1). Today’s free-range pig population in the United States is made up of feral pigs, Eurasian wild boar, and hybrid populations resulting from cross-breeding of Eurasian wild boar and feral pigs (4).
” Though there are morphological differences among the three, they are all referred to by the same scientific name and all recognized as exotic invasive species in the United States. Thus, for the purposes of this document all three subpopulations will be treated as one and will hereafter be referred to as wild pigs (1, 7, 8).”
Today there are wild pigs in 253 out of 254 Texas counties. They are present in at least 35 of the 50 states, up from 18 in 1982. There are now about 7 million wild pigs in the country, about three million of them in Texas. They are expanding their range rapidly. This is partly because of poor management and intentional release. Destruction of predators and restrictions on hunting also play a role. Pigs are highly fertile. They are able to bear early and produce litters (usually 10 piglets) up to twice a year. Although perhaps not as big an ecological threat as Florida pythons, they are destructive. Texas says:
“Wild pigs have been listed as one of the top 100 worst exotic invasive species in the world (44). In 2007, researchers estimated that each wild pig carried an associated (damage plus control) cost of $300 per year, and at an estimated 5 million wild pigs in the population at the time, Americans spent over $1.5 billion annually in damages and control costs (45). Assuming that the cost-per-wild pig estimate has remained constant, the annual costs associated with wild pigs in the United States are likely closer to $2.1 billion today (10, 11, 45).”
There are at least four ways in which pigs cause damage.
First, they root though and/or eat agriculture crops and have voracious appetites.
Second, they pollute water sources with fecal matter on a large scale.
Third, they are reservoirs for as many as thirty diseases that can be transmitted from pigs to other animals including people.
Finally, there are negative direct encounters with people. Pigs will descend on urban and suburban homes and parks eating their way across the plants, vegetables and public landscaping. Like deer, they are often involved in traffic collisions. This overlooked problem of car/animal crashes is very expensive. There are huge repair bills and loss of life to both humans and the animals involved. Pigs are opportunist eaters and predators and will consume a variety of domestic animals.
Italy, too, has a serious problem with pigs, which have moved in large numbers into Italian cities. Italians are protecting and expanding wolf populations as a partial solution. But that tactic may run into opposition here.
Both Italy and Texas are at a loss to control the upsurge in pigs. Texas has concluded that current methods including natural predation, trapping and dispatching, and aerial shooting only reduce the population by about 30 percent annually. The state estimates that 70 percent of pigs need to be dispatched just to keep the numbers steady.:
“Wild pig populations in the United States cause irreversible ecological damage and have an enormous economic impact. The extent of these economic damages are highly correlated with population size and density (14, 45). Population models indicate that the wild pig population size and range will continue to grow if left unchecked; thus, damages from wild pigs will also increase (11, 12, 14). It is estimated that annual population control efforts would need to continuously achieve 66-70% population reduction just to hold the wild pig population at its current level (14, 28). Estimates from Texas indicate that with current control methods, however, annual population reduction only reaches approximately 29% (14). The need for novel methods of wild pig population control is obvious.”