Pig (feral or wild)
Common name: pig (feral or wild)
Scientific name: Sus scrofa
Origin: Europe and Asia
This species is an established pest animal in the state of Victoria.
Read more about the classification of invasive animals in Victoria.
Impact on ecosystems and waterways
Feral pigs are considered an environmental pest due to their selective feeding, trampling and rooting for underground parts of plants and invertebrates. They also compete with native wildlife for food, water and shelter and prey directly on various wildlife species and their eggs. Feral pigs are known to prey on earthworms, insects, amphibians, reptiles, ground-nesting birds, small mammals, freshwater crayfish, frogs, turtles and their eggs.
As a consequence predation, habitat degradation competition and disease transmission by feral pigs has been listed as a key threatening process to threatened species conservation under the Environment Protection & Biodiversity Conservation Act 1999 (EPBC Act).
Feral pig activity also has a dramatic effect on watercourses and swamps. By wallowing and rooting around the waterline, they destroy the riparian vegetation which provides food and nesting sites for native wildlife and helps to prevent soil erosion. Water quality is also affected and their diggings may spread undesirable plant and animal species, and plant diseases in these areas.
Agricultural and economic impacts
Feral pigs cause significant damage in agricultural areas. They prey on newborn lambs, compete with livestock for pasture and can damage infrastructure such as fencing and water facilities. Feral pigs can reduce yields in grain, sugarcane, fruit and vegetable crops, through uprooting and consuming or trampling of plants, and their wallowing and defecation foul dams and waterholes. Feral pigs can also transport weeds and their diggings provide ideal conditions for weed establishment.
Feral pigs are known to be vectors for a number of serious endemic and exotic diseases that have the potential to devastate commercial pig operations, as well as transmit to other animals and humans. Examples include:
- foot and mouth disease virus
- Japanese encephalitis
- African swine fever.
Impact on social value and health
Feral pigs can be seen as a food and a valuable hunting resource to some members of the community. However, it is important to remember the damage caused by feral pigs to agriculture and the environment, and their ability to carry and spread of exotic diseases far outweighs any potential benefits.
Recommended control measures include:
- exclusion fencing.
The department recommends integrated pest management using all available control measures implemented in a coordinated manner at a landscape scale.
Read more about the management and control of feral pigs.
History of spread
Feral pigs in Australia is descendant of various domestic pig breeds (Sus scrofa). Feral pigs have been present in Australia since early European settlement. Most early populations were concentrated near settlement areas, though they have since spread across 45% of the mainland and occur on several offshore islands. Feral pig population have spread by natural dispersal, accidental escape and deliberate release. These populations have been able to establish, and in many cases flourish, due to their highly adaptable behaviour and their high reproductive rate.
Distribution in Victoria
Feral pigs are widespread throughout Victoria.
Feral pigs are smaller, leaner and more muscular than domestic pigs. They also have well developed shoulders and necks and smaller, shorter hindquarters than domestic pigs. Feral pig hair is more sparse, longer and coarser than domestic pigs and black is the most common colour though they can also be rusty red and of mixed colours including white, light ginger, brown and white, brown with black spots, brindle and agouti (brown or black with a lighter tip). Sometimes piglets are marked with dark longitudinal stripes, which disappear as they grow older. Feral pigs also have longer, larger snouts and tusks, smaller ears and much narrower backs. The tails of feral pigs are usually straight with a bushy tip rather than curly as is the case with domestic pigs.
Males and females differ in size and weight. Male feral pigs tend to be longer and taller than females, have larger heads, and are up to 10 to 20kg heavier when one year old. The weight of an average adult female feral pig is 50 to 60kg, with males usually weighing 80 to 100kg. However this weight can vary with habitat conditions and exceptional animals have reached up to 260kg.
Pigs have small eyes and poor eyesight, however their senses of smell and hearing are well developed.
Feral pigs restrict their activity to the cooler parts of the day at dawn and dusk and are primarily nocturnal. Feral pigs are shy animals and will avoid humans, making it easy to overlook their presence or drastically underestimate their numbers.
Feral pigs have a defined home range and regularly make use of trails between areas they use for shelter, food and water supplies. Under normal conditions the home range of adult males is 10 to 50 sq km, dry sows 10 to 20 sq km and lactating sows have restricted ranges of less than 5 sq km. When a feral pig population has an adequate food supply it is unlikely individuals will travel more than 5km outside that area except when mature crops are on offer.
Pigs must have daily access to water and wallowing sites. Feral pigs may also use pads to travel to and from water which they often mark by rubbing and tusking trees or logs, and wallowing in mud or dusty depressions. Both of these habits also help to reduce infection, while mud and dust helps to regulate body temperature.
The social structure of feral pigs is based on a matriarchal society (meaning the mothers are the leaders of the group). The most common group or 'mob' of feral pigs is called a 'sounder' which consists of related sows (mother, daughters, sisters, aunts etc) and their young. Bachelor mobs form when sexually mature males leave or are chased from their mothers group. At about 18 months males become more solitary, and they will rejoin the female groups only for mating purposes.
Mob size varies depending on the season and habitat. In forested areas a group of feral pigs will rarely exceed 12 members, while in more open country up to 40 to 50 pigs may form a herd.
Feral pigs' seasonal need for either more food, high energy or protein-rich food is often the reason for their impact on agricultural crops and is also a weakness in their ecology that can be exploited for management purposes.
Feral pigs will feed on almost anything and will switch food preferences depending on availability. Succulent green vegetation is the food item of choice, however feral pigs will eat fruit, grain, and a wide variety of animal material such as frogs, fish, reptiles, birds, small mammals and carrion. Feral pigs are known to predate on lambs and occasionally newborn calves. They will also eat underground plant material such as roots, bulbs, corms and fungi.
Shelter is important for feral pigs as it provides them with shade and protection from predators. Feral pigs typically prefer to live in moist environments that can provide a reliable and adequate food and water supply.
In Australia feral pigs are found in a wide range of habitats including:
- rainforest areas
- monsoon forest
- paperbark swamps
- open floodplains
- marsh areas
- semi-arid floodplains
- dry woodlands
- subalpine grasslands
Because feral pigs need to drink daily in hot weather they are generally not found in the dry inland areas of Australia.
The piglets of feral pigs are prone to predation by:
- wild dogs
- large birds of prey.
Diseases and parasites
Feral pigs can be hosts or vectors of a number of endemic parasites and diseases, some of which can affect animals or people. They are also a potential carrier of exotic diseases, with the biggest concern being their role as a reservoir for foot and mouth disease should it ever become established in Australia.
Under favourable conditions feral pigs can breed throughout the year in Australia, although breeding success depends on the quality and quantity of food available.
Sexual maturity in sows is dependent on weight rather than age, similar to domestic pigs. A sow may begin breeding from about six to eight months of age, when her weight exceeds about 25 to 30kg. Sows have a 21 day oestrus cycle and a gestation period of 112 to 114 days. Average litter sizes vary from 5 to 6 piglets, but up to ten piglets can be born under good conditions.
Just before giving birth, sows will make a nest using available vegetation. The nest is usually less than 2km from available water and piglets normally spend the first one to five days of their life inside the nest, with the sow inside or close by.
A feral pig litter is weaned after two or three months at which time mating can occur again. Under favourable conditions two litters can be weaned in a period of 12 to 14 months, thus feral pigs can multiply at a very fast rate. This breeding capacity allows feral pigs to quickly recover from natural setbacks or control programs, and to rapidly increase their populations in periods of favourable conditions.
A feral pig's home range is very much dependent on gender, habitat type, weather conditions and food and water availability.
Feral pigs are capable of migrating considerable distances but on a daily basis their range tends to be quite small. Home ranges vary from as little as 0.16 sq km for sows with young piglets to greater than 40 sq km for individual boars in semi-arid rangelands.
Watering points are the focus of activity for feral pig movements. In hot weather pigs may spend daytime in one area and night time spent feeding in another.
Feral pigs generally do not move very far in response to minor disturbance, including infrequent hunting by people, and usually return to their home ranges shortly afterwards. Feral pigs can shift permanently to more remote areas. If subjected to intensive or prolonged disturbance, such as large-scale hunting or other control activities.
Home ranges of individuals and groups overlap considerably. There is no evidence that feral pigs, of either gender, actively defend territories.
- Animal Control Technologies 2004, Feral Pig Problems in Australia, Animal Control Technologies, viewed online 16th March 2010
- Choquenot, D, Mxllroy, J and Korn, T 1996, Managing Vertebrate Pests: Feral Pigs, Bureau of Resource Sciences, Australian Government Publishing Service, Canberra.
- Croft, D 2007, Vertebrate Pest Control Manual: Feral pig biology and control. State of New South Wales, NSW Department of Primary Industries.
- Department of the Environment and Heritage 2004, The feral pig (Sus scrofa), fact sheet, viewed 16th March 2010.
- Invasive Animals CRC, The feral pig (Sus scofa), viewed 16th March 2010.
- Land Protection (Invasive plants and animals) 2008, Feral pigs in Queensland – distribution, ecology and impact, fact sheet, The State of Queensland, Department of Primary Industries and Fisheries.
- McGaw, C.C and Mitchell, J 1998, Pest Status Review Series: Feral Pigs (Sus scrofa) in Queensland, Department of Natural Resources and Mines, QLD
- Mitchell, J 2008, Feral Pig Control – A practical guide to pig control in Queensland, The State of Queensland Department of Primary Industries and Fisheries.
- Queensland Government Department of Natural Resources and Mines 2005, A guide to pest animal management in Queensland – Vertebrate pest manual, The State Government of Queensland, Queensland, Australia.
- Regan, K 2002, Landcare Notes: Feral pigs in Victoria, LC0306, Department of Primary Industries, State Government of Victoria.