Sus scrofa [ISC] (feral pig)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Biology and Ecology
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Impact Summary
- Economic Impact
- Environmental Impact
- Threatened Species
- Social Impact
- Risk and Impact Factors
- Similarities to Other Species/Conditions
- Prevention and Control
- Links to Websites
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Sus scrofa [ISC] Linnaeus, 1758
Preferred Common Name
- feral pig
International Common Names
- English: Eurasian wild pig; feral hog; razorback; wild boar; wild hog; wild pig
- Spanish: chancho; jabalí; porco; puerco
- French: cochon sauvage; sanglier
Local Common Names
- Germany: Wildschwein
- Portugal: javali
Summary of InvasivenessTop of page
Sus scrofa is in origin a wild pig native to large parts of Europe, Asia and North Africa. In its domesticated form as the common domestic pig, it has been taken to almost everywhere that humans live, and in many countries introduced wild populations, often large, have become established; these may be descended from escaped or deliberately released domestic pigs, wild boar introduced for hunting, escaped farmed wild boar, or a mixture of these. The species can live in a wide variety of habitats; populations can increase rapidly in suitable conditions. In many parts of its range it causes extensive damage to agriculture and natural habitats, threatens native species, and carries diseases which can affect domestic animals or humans. It may however be valued as a source of meat or as quarry for hunters. The species is listed by the IUCN SSC Invasive Species Specialist Group as one of the world’s 100 worst invasive species.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Chordata
- Subphylum: Vertebrata
- Class: Mammalia
- Order: Artiodactyla
- Suborder: Suiformes
- Family: Suidae
- Genus: Sus
- Species: Sus scrofa [ISC]
Notes on Taxonomy and NomenclatureTop of page
Sixteen species of pigs and hogs in eight genera make up the modern family Suidae. Pigs were domesticated about 10,000 years ago and wild and domestic pigs belong to the same species (Sus scrofa). Wild pigs are classified in the subspecies scrofa L. and the domestic swine in subspecies domestica L. Populations in different parts of the world consist of wild boar, the feral descendants of domestic pigs or (for example in the USA – Masterson, 2007) a mixture of the two (Long, 2003).
DescriptionTop of page
Long (2003) provides the following description: Head and body length 1100-1650 mm; tail 150-350 mm; shoulder height 550-1000 mm; weight (males) 30-190 kg (and up to 350 kg); weight (females) 15-110 kg (and up to 150 kg). Body colour varies from grey to brown or black or a mixture of colours; tusks in males to 150 mm; tail has short hairs at end; ears ovate and pointed backwards. Females with 8-14, 16 mammae; generally smaller in size and weigh less than males. Feral animals may be white, black or red or shades and mixtures, but predominantly black.
The following description is adapted from Boreal Songbird Initiative (2007), referring to North American populations: A medium-size hoofed mammal with a truncate, flexible, yet tough, cartilaginous snout disc, like that of the domestic pig. The coat is usually coarser and denser than that of the domestic pig and has a dense undercoat in winter. This species is extremely variable in colour. It is most often black, but may be brown, grey, or black and white. The tail is moderately long, lightly haired, and hangs straight, not coiled like that of the domestic pig. The upper tusks (modified canines), are usually 75-125 mm long but can be up to 230 mm long; they curl out and up along the sides of the mouth. The lower canines are smaller, turn out slightly whilst rising outside the mouth and point back toward the eyes. Skulls are identifiable by the lack of a bony ring around the sockets and by the tall, steep form of the cranium (Lowery, 1974; Whitaker, 1988; both cited in Masterson, 2007). The young have pale longitudinal stripes on their body until they are 6 weeks of age. The adults’ height is up to 900 mm; the length is 1320-1820 mm. Males weigh from 75 to 200 kg whilst females weigh from 35 to150 kg. The life span is generally 15 to 25 years. Nowak (1991, cited in Masterson, 2007) reports that domestic pigs can reach 450 kg and their feral counterparts are of the same order of size.
Several millennia of selective breeding have yielded a domesticated animal that is morphologically quite distinct from the original wild type (Masterson, 2007). Wild and domestic subspecies can interbreed and have done so over time (Whitaker, 1988): The greater the percentage of wild boar genes a feral pig contains, the more it will resemble the wild type in appearance, typically bearing a bristly coat and mane, a straight tail, and impressive tusks (Whitaker 1988).
DistributionTop of page
Domestic pigs are found in most countries, but this datasheet confines itself to wild and feral populations (except where information about domestic pigs is relevant to their wild or feral counterparts).
Wild Sus scrofa are native to large parts of Europe, Asia and North Africa; they have become extinct over much of the former range of the species, including southern Scandinavia, the Nile valley and Britain (Tisdell, 1982), but have recently been reintroduced to parts of their former range – for example in the UK and Sweden where they have escaped from farms (Wilson, 2005; Truvé and Lemel, 2003). Introduced populations, descended from domestic pigs, wild boar or a combination of the two, are present in many parts of the world.
In South America, the feral pig (Sus scrofa scrofa) is an introduced species in Brazil, imported from Uruguay and Argentina in the 1980s and more recently (1997) from France and Canada, but there are also wild feral pigs descended from domestic pigs introduced in previous centuries (Grossi et al., 2006).
Feral pigs occur in all US states around the Gulf of Mexico, including Florida (Whitaker, 1988, cited in Masterson, 2007), and in other parts of the USA (NatureServe, 2013; Barrett and Birmingham, 2005). Belden (1993), cited in Masterson (2007) states that, within the USA, Florida's feral pig population is second only to that of Texas.
The recent expansion in feral pig distribution in Australia has been attributed to the increase in suitable habitats, in particular, an increase in water availability from farm dams and development of forest industries (Spencer and Hampton, 2005).
Further information on introduced pig populations, including a table of islands where they have been introduced, can be found in Long (2003).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Christmas Island (Indian Ocean)||Present||Introduced||SPREP, 2000|
|Georgia (Republic of)||Present||Native||IUCN, 2012|
|Indonesia||Present||Present based on regional distribution.|
|-Irian Jaya||Present||Native||IUCN, 2012|
|-Nusa Tenggara||Present||Native||IUCN, 2012|
|Korea, DPR||Present||Native||IUCN, 2012|
|Korea, Republic of||Present||Native||IUCN, 2012|
|Malaysia||Present||Present based on regional distribution.|
|-Peninsular Malaysia||Present||Native||Invasive||Ickes, 2001; Ickes et al., 2001; Ickes et al., 2005||At much higher than natural density|
|Pakistan||Present||Native||Ahmad et al., 1995; IUCN, 2012|
|Sri Lanka||Present||Native||IUCN, 2012|
|Egypt||Eradicated||Native||Oliver et al., 1993; IUCN, 2012||Extinct about 1902|
|Libya||Eradicated||Native||Oliver et al., 1993; IUCN, 2012||Last reported in 1880s|
|Mauritius||Present||Introduced||Invasive||Carter and Bright, 2002|
|South Africa||Present||Introduced||Invasive||Long, 2003|
|Sudan||Absent, unreliable record||Introduced||Kingdon, 1997||Needs confirmation|
|Canada||Present||Present based on regional distribution.|
|Mexico||Present||Introduced||Invasive||Zavaleta, 2002; Long, 2003|
|USA||Present||Present based on regional distribution.|
|-California||Present||Introduced||Invasive||Schuyler et al., 2002; Barrett and Birmingham, 2005||Eradicated on Santa Rosa Island|
|-Florida||Present||Introduced||Invasive||Barrett and Birmingham, 2005; NatureServe, 2013|
|-Georgia||Present||Introduced||Invasive||Barrett and Birmingham, 2005; NatureServe, 2013|
|-Hawaii||Present||Introduced||Invasive||SPREP, 2000; Barrett and Birmingham, 2005; Rusz, 2007|
|-Kansas||Present||Introduced||Invasive||Gipson et al., 2006|
|-Louisiana||Present||Introduced||Invasive||Barrett and Birmingham, 2005; Rusz, 2007|
|-Nebraska||Present||Introduced||Invasive||Gipson et al., 2006|
|-New Mexico||Present||Introduced||NatureServe, 2013|
|-North Carolina||Present||Introduced||Invasive||Barrett and Birmingham, 2005; NatureServe, 2013|
|-South Carolina||Present||Introduced||Invasive||Dewey and Hruby, 2002|
|-Tennessee||Present||Introduced||Invasive||Barrett and Birmingham, 2005; NatureServe, 2013|
|-Texas||Present||Introduced||Invasive||Barrett and Birmingham, 2005; NatureServe, 2013|
|-West Virginia||Present||Introduced||NatureServe, 2013|
Central America and Caribbean
|Antigua and Barbuda||Present||Introduced||IUCN, 2012|
|Bahamas||Present||Introduced||Invasive||Kairo et al., 2003||Established|
|Curaçao||Present||Introduced||Invasive||Kairo et al., 2003|
|Dominica||Present||Introduced||Invasive||Kairo et al., 2003||Established|
|Dominican Republic||Present||Introduced||IUCN, 2012|
|Jamaica||Present||Introduced||Invasive||Kairo et al., 2003||Established|
|Puerto Rico||Present||Introduced||Invasive||Kairo et al., 2003; Barrett and Birmingham, 2005||Established|
|Saint Lucia||Widespread||Introduced||Invasive||Caribbean Conservation Association, 1991; Organisation of Eastern Caribbean States, 2012||Widespread and invasive in forests; threatens some rare birds and the endemic herpetofauna; control efforts would require simultaneous halt to re-supply through continued escapes.|
|United States Virgin Islands||Present||Introduced||Invasive||Kairo et al., 2003; Barrett and Birmingham, 2005|
|Argentina||Present||Introduced||Invasive||Jaksic et al., 2002; Novillo and Ojeda, 2008||Established|
|Brazil||Present||Introduced||Invasive||Sicuro and Oliveira, 2002; Long, 2003||Established|
|Chile||Present||Introduced||Invasive||Jaksic et al., 2002||Established|
|Uruguay||Present||Introduced||Grossi et al., 2006|
|Cyprus||Present||Introduced||Hadjisterkotis, 2004; IUCN, 2012||Introduction in 1990 for game farming|
|Czech Republic||Present||Native||IUCN, 2012|
|France||Present||Native||Cargnelutti et al., 1992|
|Ireland||Present, few occurrences||Invasive||IUCN, 2012; McDevitt et al., 2013||Wild boar originally native but eradicated some centuries ago. Initial genetic studies indicate that recently introduced animals are descended mainly from domestic pigs|
|Italy||Present||Native||Boitani et al., 1995|
|Norway||Localised||Rosvold and Andersen, 2008||Extinct since prehistoric times; recently spread from Sweden|
|Russian Federation||Present||Native||IUCN, 2012|
|San Marino||Present||Native||IUCN, 2012|
|Sweden||Localised||Truvé and Lemel, 2003||Originally native; exterminated in 16th century and reintroduced in recent decades|
|UK||Localised||Wilson, 2005; Frantz et al., 2012; Goulding, 2012||Wild boar originally native; exterminated some centuries ago, and recently re-established following escapes from farms. Genetic studies of one population indicate a mixture of wild boar and domestic pig ancestry.|
|American Samoa||Present||Introduced||Invasive||SPREP, 2000|
|Australia||Present||Introduced||Invasive||Dexter, 2003; Spencer and Hampton, 2005||Established and range expanding.|
|-Australian Northern Territory||Present||Introduced||Invasive||Twigg et al., 2005|
|-Lord Howe Is.||Eradicated||Introduced||Parkes et al., 2002|
|-New South Wales||Present||Introduced||Invasive||Hone and Waithman, 1979|
|-Queensland||Present||Introduced||Invasive||Clarke et al., 2000|
|-South Australia||Present||Introduced||Invasive||Clarke et al., 2000|
|-Victoria||Present||Introduced||Invasive||Clarke et al., 2000|
|-Western Australia||Present||Introduced||Invasive||Clarke et al., 2000; Burbidge and Morris, 2002|
|Cook Islands||Present||Introduced||Invasive||SPREP, 2000|
|French Polynesia||Present||Introduced||Invasive||SPREP, 2000||Established|
|Marshall Islands||Unconfirmed record||Introduced||SPREP, 2000|
|Micronesia, Federated states of||Present||Introduced||Invasive||SPREP, 2000|
|Nauru||Unconfirmed record||Introduced||SPREP, 2000|
|New Caledonia||Present||Introduced||Invasive||SPREP, 2000; Pascal et al., 2006||Established in some parts|
|New Zealand||Present||Introduced||Invasive||Torr, 2002||Present and controlled. Eradication on Kapiti, Raoul and Aorangi islands|
|Niue||Unconfirmed record||Introduced||SPREP, 2000|
|Northern Mariana Islands||Present||Introduced||Invasive||SPREP, 2000; Kessler, 2002|
|Papua New Guinea||Present||Introduced||Invasive||SPREP, 2000||Established|
|Pitcairn Island||Absent, reported but not confirmed||Introduced||SPREP, 2000|
|Solomon Islands||Present||Introduced||Invasive||SPREP, 2000||Extinct on Rennell Island|
|Tuvalu||Unconfirmed record||Introduced||SPREP, 2000|
|Wallis and Futuna Islands||Present||Introduced||Invasive||SPREP, 2000|
History of Introduction and SpreadTop of page
Pigs were among the first mammals to be domesticated by man, beginning in China some 7000 years ago and possibly dating further back to 10,000 BC in the region that is now Thailand (Nowak, 1991, cited in Masterson, 2007). They have been introduced virtually everywhere that humans have gone, and established wild populations in many places.
Masterson (2007) states that: ‘The first intentional introduction to the present-day USA may have been intentional introduction of domestic hogs to the Hawaiian Islands by Polynesians perhaps 1000 years ago (Nowack [Nowak], 1991). The first introduction of domestic hogs to the continental US is historically documented. A vessel captained by the Spanish explorer Hernando De Soto and carrying domestic hogs destined for the New World landed on the Gulf coast in 1539 (Lowery, 1974; Gingerich, 1994). .... Feral pigs currently found within the USA represent a combination of descendant lines from European wild boars originally released for sport hunting purposes and feral animals derived from escaped domestic pigs .... (Whitaker, 1988)’.
In New Zealand, Captain Cook presented some pigs to the Maori and released others during his second and third voyages between 1773 and 1777. The first official introduction to Australia was with the First Fleet in 1788. Once established, colonies of feral pigs built up rapidly in many areas. Estimates of population size vary between 3.5 million and 23.5 million, inhabiting 38% of Australia, but their distribution and abundance can vary greatly from year to year and are dependent on environmental conditions (Choquenot et al., 1996).
Further information on the introduction of pigs around the world can be found in Long (2003).
IntroductionsTop of page
|Introduced to||Introduced from||Year||Reason||Introduced by||Established in wild through||References||Notes|
|Natural reproduction||Continuous restocking|
|Australia||Europe||1788||Food (pathway cause)||Yes||Diong (1982)||With the First Fleet arriving in Australia. Captain Cook released pigs in Tasmania 1777 (Diong, 1982)|
|New Zealand||Europe||before 1784||Food (pathway cause)||Diong (1982)||Released by Captain Cook|
|USA||Europe||1500 onward||Food (pathway cause)
Hunting, angling, sport or racing (pathway cause)
|Yes||Towne and Wentworth (1950)||Christopher Colombus first introduced pigs into North America in 1493 in the West Indies.|
Risk of IntroductionTop of page
Pigs are very versatile and are spreading very quickly in the areas in which they have been (re)-introduced. Their range is constantly increasing (e.g. in Australia and New Zealand). Deliberate introductions have occurred for sport hunting purposes, and according to Wilson (2005) wild boar have escaped from farms. Domestic pigs are present in most parts of the world, but their presence does not always result in the establishment of feral populations.
HabitatTop of page
The feral pig can adapt to a variety of environments, from Mediterranean oak woodland forests to the semi-arid rangelands of Eastern Australia, from the flood plains, billabongs and grassland savannas of tropical north-western Australia to the grey beech forests of the Smoky Mountains in America, and from the wetland and lowland evergreen monsoon forests of Australia to the fresh water marshes and brackish water marshes of South Carolina (Wood and Brenneman, 1980, cited in Wolf and Conover, 2003). Wild pigs are rarely found at altitudes over 1650m (Hide, 2003), but are known to be found at altitudes as high as 3000 m in New Guinea (Hide 2003). (Paragraph adapted from ISSG, 2013).
The typical wild habitat is generally moist forests and shrublands. Pigs are limited by maximum winter snowfall and severe temperature changes, as deep snow decreases their ability to travel and find food. Low temperatures will cause discomfort. Conversely, they are prone to sunstroke in unusually warm temperatures, and have developed the technique of wallowing in mud or water to maintain a comfortable temperature in hotter climates. Wallowing also protects against sunburn and insect bites. In dry and hot climates, they will only become established if water supplies are adequate to allow survival (Gingerich, 1994). (Paragraph adapted from Dewey and Hruby, 2002).
Habitat ListTop of page
|Terrestrial – Managed||Cultivated / agricultural land||Present, no further details|
|Managed forests, plantations and orchards||Present, no further details|
|Managed grasslands (grazing systems)||Present, no further details|
|Disturbed areas||Present, no further details|
|Terrestrial ‑ Natural / Semi-natural||Natural forests||Present, no further details|
|Natural grasslands||Present, no further details|
|Riverbanks||Present, no further details|
|Wetlands||Present, no further details|
|Scrub / shrublands||Present, no further details|
|Arid regions||Present, no further details|
|Coastal areas||Present, no further details|
|Mud flats||Present, no further details|
Biology and EcologyTop of page
Domestic swine (Sus scrofa domestica) normally present 2n = 38 and wild pigs (Sus scrofa scrofa) 2n = 36 (Bosma, 1976). Despite these differences in chromosome number, these animals can mate and produce fertile hybrids. Hybrids have 37 chromosomes, and are morphologically similar to wild pigs (Lui, 2000). Hybrids can successfully breed with wild and domestic pigs or with other hybrids, generating offspring with 36, 37 or 38 chromosomes (Lui, 2000; Grossi et al., 2006).
For studies of genetic differentiation, mitochondrial DNA (mtDNA) is used as a tool to characterize races and determine genetic relationships (Grossi et al., 2006; Watanobe et al., 1999).
According to Masterson (2007): ‘In temperate regions breeding in S. scrofa is confined to the spring, whereas in subtropical climates the breeding season is protracted. In the tropics, breeding can occur throughout the year. Regardless of location, [peak] breeding coincides with the rainy season (Nowak, 1991). Both sexes usually reach sexual maturity in the first year of life, between 8-12 months in males and as early as 5-8 months in females (Johnson et al., 1982). Despite early onset of maturity, female feral pigs usually do not breed before 18 months of age, while males tend not to achieve reproductive success until they are fully grown, at approximately age five. The oestrous cycle of female pigs is approximately 21 days (Ingles, 1965). Adult males are solitary outside the breeding season, while females and juveniles are gregarious (Gingerich, 1994). Females leave the group to nest and give birth. This nesting behaviour is atypical of ungulate (hoofed) mammals. Litters usually consist of between 3 and 12 young and females generally produce one or two litters each season throughout their reproductive lives (Ingles, 1965; Gingerich, 1994). Gestation varies between 100 and 140 days. Young are weaned in 3-4 months and often leave their mother before the next litter if the mother produces multiple litters in a breeding season (Nowak, 1991). Early mortality rates can be high. Baber and Coblentz (1986) reported that 58% of piglets died before weaning.’
The sow and her young forage in a family group, usually of about half a dozen animals, but they sometimes join other groups in herds of up to 50 individuals. Except during the breeding season, mature males are solitary or band in small groups. In the breeding season, males gather as females enter oestrus; they fight for dominance and dominant males mate first (Boreal Songbird Initiative, 2007).
Physiology and Phenology
According to Masterson (2007): ‘Feral pigs occur from temperate climates to the tropics and their activity patterns are tied to the temperature regimes of the various climates in which they are found. These mammals lack sweat glands and rely greatly on behavioural means of body temperature regulation (Gingerich, 1994). In hot, tropical climates, peak activity occurs in the early morning and late afternoon (Diong, 1982), or during the night (Sekhar, 1998). In temperate regions with pronounced seasonal variation, peak activity times and foraging areas change to take advantage of biologically favourable temperatures (Belden and Pelton, 1975). For example, feral pigs on California's Santa Cruz Island are most active at midday during wet winter months, and at night during the warm, dry summer (Vuren, 1984). Feral pigs will only become established in hot climates if water supplies are adequate to allow survival (Gingerich, 1994).’
Smell is by far the most advanced of the pig's senses. A large round disk of cartilage is connected to muscle that gives the snout extra flexibility. S. scrofa also has an advanced sense of taste. They are quick to identify unknown objects by tasting. It is believed that they lack good eyesight. The eyes are positioned on the sides of the head, restricting their forward vision (Nowak, 1991, cited in Dewey and Hruby, 2002).
Life span is generally 15 to 25 years (Boreal Songbird Initiative, 2007).
See first paragraph under ‘Physiology and Phenology’.
Pigs and wild boar are opportunistic omnivores, feeding on all types of organic matter. Ballari and Barrios-García (2013) review the literature on the diet of wild boar in the native and introduced range. The exact composition of the diet varies between different studies; it consists mostly of plant matter (including bulbs, roots, aerial parts, plants and seeds), but the proportion of animal matter and fungi is greater in the introduced range. Food items frequently include agricultural crops (especially in the native range) and endangered animal species (especially in the native range).
Feral pigs in North America and presumably elsewhere use their tusks and snouts to root through the ground in search of roots, tubers, bulbs, worms, insects, slugs and snails. In temperate areas where oaks are common, they will consume fallen acorns and other nuts, but also frogs, lizards and snakes, rodents and other vulnerable mammals. They are also known to consume bird eggs, nestlings and burrowing adult birds (Lowery, 1974; Bratton et al., 1982; Laycock, 1984; Baber and Coblentz, 1987; Gingerich, 1994). Their feeding activity can impact population densities of preferred prey (Meads et al., 1984). They are highly adaptable and opportunistic in terms of diet, and seasonal dietary shifts occur as food items become either scarce or more abundant. Wood and Roark (1980) reported that populations in South Carolina feed on acorns, fruits and nuts in the autumn and winter, shifting in spring to foliage and herbaceous vegetation and later on in summer to tubers and roots. As a result of these dietary shifts, the degree of destructiveness caused by rooting can also vary by season. (Paragraph adapted from Masterson, 2007).
In temperate climates, acorns are a staple, but Sus scrofa also feed on beech, hickory, and pecan nuts and any other fruit or berry they may find. They also forage in swamps and marshes. They rely on a wide variety of vegetation, including roots, tubers, grasses, fruit, and berries, but they also eat crayfish, frogs, snakes, salamanders, mice, the eggs and young of ground-nesting birds, young rabbits, and any other easy prey or carrion encountered while foraging (Boreal Songbird Initiative, 2007). They have been known to kill and eat fawns or lambs (Pavlov and Hone, 1982).
See ‘Habitat’ section.
ClimateTop of page
|A - Tropical/Megathermal climate||Tolerated||Average temp. of coolest month > 18°C, > 1500mm precipitation annually|
|C - Temperate/Mesothermal climate||Preferred||Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C|
|D - Continental/Microthermal climate||Tolerated||Continental/Microthermal climate (Average temp. of coldest month < 0°C, mean warmest month > 10°C)|
Notes on Natural EnemiesTop of page
Although adult pigs are safe from most predators other than man, young animals are reportedly vulnerable (in North America and presumably elsewhere) to predators such as eagles and hawks, owls, foxes, bobcats (Lynx rufus) (Laycock, 1984; Gingerich, 1994), bears and feral dogs (Boreal Songbird Initiative, 2007). In south Florida, panthers (Felis concolor) are capable of taking adult pigs as prey (Gingerich, 1994). (Paragraph adapted from Masterson, 2007).
Means of Movement and DispersalTop of page
The feral pig is a fast runner and a good swimmer. It usually trots from one foraging area to another, and then slows to a walk. It seldom wanders beyond an area of 26 km² if food is abundant, but may extend its range to up to 130 km² when forage is poor (Boreal Songbird Initiative, 2007).
In Australia, feral pigs have been recorded moving 20 km in 48 h when exposed to food shortage (Auld and Tisdell 1986).
Pigs have been introduced to most parts of the world as domestic animals, and often become feral; wild boar have also been introduced for farming (in some cases they have escaped and formed wild populations) or released for hunting.
Impact SummaryTop of page
|Cultural/amenity||Positive and negative|
|Economic/livelihood||Positive and negative|
|Environment (generally)||Positive and negative|
|Human health||Positive and negative|
Economic ImpactTop of page
The World Conservation Union's Invasive Species Specialist Group (ISSG, 2013) lists feral pigs as among "100 of the world's worst invasive alien species" and recognizes them as potentially major drivers of extinction and ecosystem change. Feral pigs cause agricultural damage through predation of newborn lambs, reduction in crop yields, damage to fences and water sources, and competition with stock for feed by consuming or damaging pasture. They also are considered a major threat to stock as a potential carrier of exotic diseases. The major concern in Australia and New Zealand is their role as a reservoir host of foot-and-mouth disease should the disease ever become established there. However, they are also an economic resource for game meat, an industry that is worth approximately $20 million a year (Choquenot et al., 1996).
Landowners and farmers regularly report damage and loss due to feral pig activity. Food crops like corn, oats, wheat and, soybeans are attacked, as are young trees planted in silviculture operations. Home gardens often suffer damage. In 1998 in California, it was estimated that the economic loss resulting from pig rooting was $1.73 million (Frederick, 1998, cited in Masterson, 2007).
Feral pigs represent also a potential source of disease in humans and animals. They carry Aujeszky's disease, a viral swine disease of considerable economic importance to the pork industry. Cattle are susceptible as secondary hosts, and infection results in the cattle disease known as mad itch. Rats, dogs, horses and wild animals like panthers are also secondary hosts (Fenner et al., 1993; Gingerich, 1994). Feral pigs also carry trichinosis and swine brucellosis which is potentially fatal in humans (Gingerich, 1994). Leptospirosis, foot-and-mouth disease, Japanese encephalitis and the parasite Toxoplasma gondii are other disease agents harboured by feral pigs (Tolleson et al., 1995; Hampton et al., 2004; Gauss et al., 2005). Feral pigs were also implicated in an outbreak of Escherichia coli spinach contamination in California in 2006 that killed at least three people. The proposed infection pathway suggests that feral pigs transmitted the pathogenic E. coli strain to spinach fields from adjacent cattle pastures. (Paragraph adapted from Masterson, 2007).
Feral pigs have long been implicated as potential vectors in the spread of the devastating plant pathogen Phytophthora cinnamomi due to their rooting and wallowing activities which may predispose them as vectors of infested soil. A recent study showed that they also have the ability to transport viable P. cinnamomi in their digestive tract (Li et al., 2014).
Environmental ImpactTop of page
Impact on Habitats
As omnivores, feral pigs are responsible for many adverse effects; threatening native fauna and flora, and changing ecosystem dynamics (Challies, 1975; Cruz and Cruz, 1987; Drake and Pratt, 2001; Roemer et al., 2002; Vtorov, 1993). Their feeding activities impact on other endemic animal species and on vegetation. According to Masterson (2007): ‘The destructive rooting habits of feral pigs make them particularly problematic invaders. Rooting digs up and overturns sizable patches of earth, destroys vegetation and seed banks, exposes tree roots and increases soil nutrient leaching (Kotanen, 1995; Singer et al., 1984; Arrington et al., 1999).’
Habitat alteration may include loss of native vegetation and spread of opportunistic weeds into newly disturbed areas. A study by Singer et al. (1984) monitoring feral pigs within the Great Smoky Mountains National Park in the eastern USA reports that their destructive foraging exposed several thousand tree roots per hectare, reduced plant cover by as much as 80%, and increased bare ground by nearly 90%. Forest litter and soil bulk density were also greatly reduced while erosion and nutrient loss from the forest floor were doubled (see also Peine and Farmer, 1990). (Paragraph adapted from Masterson, 2007).
A study in Argentina by Barrios-Garcia and Simberloff (2013) showed that in three different plant communities, rooting by introduced wild boar promoted establishment of seedlings of non-native species.
Where feral pigs occur in association with wetlands and coastal marshes, pig foraging may add to the loss of diversity and destroy the already fragile ecosystem (Masterson, 2007).
Barrios-Garcia and Ballari (2012) review the literature on the impact of wild boar in the native and introduced ranges, including the identification of gaps in knowledge where further research is needed.
Impact on Biodiversity
A literature review by Ballari and Barrios-García (2014) found reports of predation of endangered animal species by introduced wild boar.
In some islands in the Pacific, wild pigs are reported to be effective predators of both surface and burrow-nesting seabirds: they eat eggs, nestlings and adults of birds such as sooty terns (Sterna fuscata), and dig out the burrows of petrels, dark-rumped petrels (Pterodroma phaeopygia) and potentially other species such as albatrosses, shags and boobies. They impact on other species such as earthworms and snails by destroying their habitat, and damage native forests by digging seedlings and other plants, and spreading seeds of weeds in their droppings (SPREP, 2000).
In the USA, species such as northern short-tailed shrews (Blarina brevicauda), southern red-backed voles (Clethrionomys gapperi or Myodes gapperi), and red-cheeked salamander (Plethodon jordani) are at risk (Laycock, 1984; Singer et al., 1984) where feral pigs occur. Endemic herbaceous vegetation such as Clingman's hedgenettle (Stachys clingmanii) and Virginia chain fern (Woodwardia virginica) may also be impacted (Bratton et al., 1982). Ground nesting birds and other species may be negatively impacted. (Paragraph adapted from Masterson, 2007).
Masterson (2007) further states that:
‘In Hawaii, feral pigs kill several native tree species (by felling or ring-barking them) in pursuit of native tree ferns that are a dietary staple (Diong, 1982). On Santiago Island in Ecuador, egg predation by feral pigs has reduced giant tortoise and sea turtle population numbers (MacFarland et al., 1974; Green and Ortiz, 1982; Coblentz and Baber, 1987).
Where feral pigs occur in association with wetlands and coastal marshes, pig foraging may add to the loss of diversity and destroy the already fragile ecosystem. There is at least some indication, however, that plant diversity may actually increase on localized scales in response to disturbance by pigs, e.g., if pioneering species move into areas that have been upturned by rooting pigs (Arrington et al., 1999; Ford and Grace, 1998).’
Phytophthora cinnamomi, a fungus which feral pigs can spread in infected soil (due to their rooting and wallowing activities) or as recently shown in their digestive tract (Li et al., 2014), is an important pathogen of native wild plants as well as crops. The physical damage caused by foraging pigs, in combination with the dispersal of an, as yet, unidentified Phytophthora species, are considered the major biological threats to the critically endangered conifer Agathis montana in New Caledonia (Tron and Sabran, 2014).
Threatened SpeciesTop of page
|Threatened Species||Conservation Status||Where Threatened||Mechanism||References||Notes|
|Agathis montana (Mount Panié kauri)||CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered)||New Caledonia||Pest and disease transmission; Rooting||Tron and Sabran, 2014|
|Blarina brevicauda||LC (IUCN red list: Least concern) LC (IUCN red list: Least concern)||USA||Masterson, 2007|
|Clethrionomys gapperi||LC (IUCN red list: Least concern) LC (IUCN red list: Least concern)||USA||Masterson, 2007|
|Plethodon jordani||NT (IUCN red list: Near threatened) NT (IUCN red list: Near threatened)||USA||Masterson, 2007|
|Pterodroma phaeopygia (Galapagos dark-rumped petrel)||CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered); USA ESA listing as endangered species USA ESA listing as endangered species||Galapagos Islands||Predation||SPREP, 2000|
Social ImpactTop of page
Sus scrofa carries parasitic infections transmissible to humans through eating undercooked pork and through contact, including trichinosis, cysticercosis, brucellosis and toxoplasmosis (Masterson, 2007; Dewey and Hruby, 2002; Gauss et al., 2005). They have also been implicated in an outbreak of human Escherichia coli infection in California (Masterson, 2007). Both domesticated and wild pigs can be quite aggressive, at least when threatened.
Risk and Impact FactorsTop of page Invasiveness
- Invasive in its native range
- Proved invasive outside its native range
- Has a broad native range
- Abundant in its native range
- Is a habitat generalist
- Capable of securing and ingesting a wide range of food
- Highly mobile locally
- Long lived
- Fast growing
- Has high reproductive potential
- Ecosystem change/ habitat alteration
- Increases vulnerability to invasions
- Negatively impacts agriculture
- Negatively impacts human health
- Negatively impacts animal health
- Reduced native biodiversity
- Threat to/ loss of endangered species
- Threat to/ loss of native species
- Pest and disease transmission
- Interaction with other invasive species
- Highly likely to be transported internationally deliberately
- Difficult/costly to control
UsesTop of page
Domestic pigs are very widely used as a source of meat and other products. Wild boar and feral pigs are, in parts of their range, valued as a source of meat, as quarry for sport hunting, or as wildlife. Wild boar are sometimes farmed for their meat.
Similarities to Other Species/ConditionsTop of page
Sus scrofa could be confused with the peccaries of the Americas, the most widespread of which is the collared peccary (Pecari tajacu). However, the latter is much smaller, and more uniformly and thickly coated; it is greyish, usually with a light collar over the shoulders; and it has a vestigial tail and upper tusks that point down (Boreal Songbird Initiative, 2007).
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Pigs have been successfully eradicated from a number of islands in New Zealand, California and the Galapagos; see below under ‘IPM’ for more information.
Regulations differ from one country to another. In some cases, landowners can be held responsible for population control. In others, where the species has been introduced and is considered as a pest (e.g., Australia and New Zealand), regulations at the state or federal levels are in place and control programmes (air-shooting, poisoning, etc.) are developed to keep population numbers down and to limit spread.
Shooting from helicopters is efficient and provides a quick knockdown. Pig populations can recover rapidly between shooting and poisoning episodes. Shooting from the ground, with or without dogs, is generally considered to play an insignificant role in damage control except where it is intensively conducted on small accessible populations. Populations can recover between shooting episodes (Invasive Animals Cooperative Research Centre, 2012). New Zealand conservation practitioners have in the past applied mainland hunting techniques to eradicate feral pig populations from small islands <200 ha) (Veitch and Bell, 1990, cited in Cruz et al., 2005).
Trapping can be effective, but results are variable, being affected by season, trap type and site, pre-baiting techniques and trapping frequency. An advantage of trapping is that it can be fitted into routine property activities and the trapped animals sold to the game meat market (Invasive Animals Cooperative Research Centre, 2012).
In Hawaii, snaring has been used to control pigs within 600–800 km² fenced enclosures located in remote areas of rain forest (Anderson and Stone, 1993).
According to Choquenot et al. (1996), there were at that date no biological control (or fertility control) agents suitable for use against feral pigs.
Poisoning techniques have been developed to control or eradicate feral pig populations (Choquenot et al., 1996; Cruz et al., 2005). Poisoning using 1080 (sodium fluoroacetate) with anti-emetics such as metoclopramide, thiethylperazine and prochlorperazine in grain or meat baits, is used in some rural communities to manage the damage due to feral pigs (O'Brien et al., 1986, in Wolf and Conover, 2003). Poisoning requires appropriate free-feeding with non-toxic bait to attract pigs before the poison bait is used. Free-feeding also helps to reduce the risk of loss to non-target animals. Populations can recover between poisoning episodes (Invasive Animals Cooperative Research Centre, 2012).
The best results have been obtained from integrated management using a range of control techniques (Choquenot et al., 1996).
Hunting and poisoning techniques used in combination have been used for pig eradication efforts on islands, for example in California and New Zealand (Lombardo and Faulkner, 2000; Schuyler et al., 2002; Veitch and Bell, 1990, cited in Cruz et al., 2005; Veitch and Clout, 2002).
Wild pigs have been successfully eradicated from Santiago Island in the Galapagos Archipelago (off the coast of Ecuador) and much can be learnt from this experience. Successful eradication of the feral pig on the island was due to a sustained effort using an effective poisoning campaign doubled with a hunting program throughout the island. In 2000, the last pig present on the island was poisoned. A sustained monitoring effort was critical to successful eradication. The lack of such an effort is responsible for many eradication failures (Cruz et al., 2005).
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11/08/2010: Original text by:
CRCNPB Australia, Canberra, Australia.
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