Pig facts

●    Pigs are found on every continent except Antarctica, but are an invasive species in many countries
●    Pigs are smart and can use their senses and memories to find food and solve puzzles
●    Domesticated pigs have even been trained to respond to commands and can tell people apart by sight or sound
●    Only domesticated pigs have curly tails
●    Pigs have very varied diets – some even forage on beaches for turtle eggs
●    They can be aggressive, particularly when in large numbers, and have been known to chase off leopards

Domesticated pigs (Sus domesticus) are descendents of various species of wild swine, including the Eurasian pig (Sus scrofa), Sulawesi warty pig (Sus celebensis) and bushpig (Potamochoerus larvatus).³ As humans transitioned to agricultural lifestyles, they domesticated pig species local to their region. The first pigs may have been domesticated in the Near East around 10,000 to 11,000 years ago.⁴

The Eurasian pig, also known as the wild boar, is by far the most common and widely domesticated pig. The wild boar has been a primary food source for hunter-gatherers and agriculturalists for thousands of years. It is found on all continents bar Antarctica, either natively or in feral form, having in most cases been introduced by humans. In many countries, the wild boar is considered a pest owing to the damage it can do to crops. 

Domesticated pigs are recognisable by their short, sometimes very sparse, fur and relatively shorter teeth. They also have much shorter tusks compared with wild species. Farm pigs also show other signs of domestication, such as floppy ears and curly tails. Although some breeds can weigh as much as 180kg and live for up to 27 years, farm pigs rarely reach these sizes or ages, and are often slaughtered while weighing less than 100kg when they're less than a year old.⁵

Wild pigs can vary greatly in size and weight. The heaviest breed, the wild boar, can reach 320kg, while the smallest, the pygmy hog (Sus salvanius), weighs less than 10kg. The giant forest hog (Hylochoerus meinertzhageni) can grow to 1.3-2m (4.3-6.6ft) long and 0.75-1.1m (2.5-3.6ft) tall. Giant forest hogs, like most wild hogs, have shorter lifespans than domesticated breeds; but while the average lifespan is five years, they have been known to live for up to 18 years.⁶

Wild pigs are sociable and typically form herds of between six and 20 individuals. These tend to be made up of one adult female, her most recent litter and some adolescents from previous litters. During mating season, males often join these family groups to mate with the female.

Litter sizes are highly variable and depend on factors such as the weather, the length of the breeding season and food availability. However, they commonly contain between two and 10 individuals.⁷

Pigs and their wild relatives, hogs and boars – collectively known as swine – are among the most wide-ranging and adaptable mammals on the planet. They can be found in all sorts of habitats, from the beaches of tropical islands to dense, swampy rainforests, mountainous woodlands and hot, dry savannahs.⁸

Swine all belong to the family Suidae. Their nearest non-pig relative is the peccary, an animal native to the Americas that is sometimes called a skunk pig.

Swine can be found on all continents except Antarctica, but are only native to Asia, Africa and Europe. Some domesticated pigs have become invasive species in the Americas and Australasia, where they are called feral pigs, hogs or boars and are treated as pests.⁹

Pigs have a reputation for having a big appetite, and for good reason – both domestic and wild pigs have broad diets.¹⁰ While up to 90% of their diet is made up of plants – including roots, shoots, leaves and fruits – they will also eat animals, like insects, small invertebrates and the carcasses of deceased large animals.¹¹ In coastal areas, pigs have also been known to eat crabs, sea turtle eggs and fish.¹²

There have been anecdotal stories of pigs eating goats and deer fawns and even chasing a leopard away from a buffalo calf it had killed in order to feast on it themselves. While such accounts are hard to verify, they are frequent enough to suggest that some larger pigs are able to take on bigger prey when they work together.

The small amount of animal protein pigs eat is essential to their diet. Domestic pigs denied meat in experimental conditions lost weight.

Feeding is a communal activity and an opportunity for solitary males to join bigger groups to socialise, mate and fight. Pigs spend about eight hours a day feeding and can travel up to 15km (9.3 miles) doing so. Most activity is undertaken at night, dusk or dawn. 

Their appetite for fruit means pigs are important ecosystem engineers, helping to disperse seeds and nuts around their forest homes. Their importance to the maintenance of forests has led to the call for wild breeds to be reintroduced to forests in the UK and Sweden, where they were once native before being hunted to extinction.

Pigs have adapted to a wide variety of habitats. We might think of them as most at home in a mud bath, but some species are equally happy frolicking in the surf of a Caribbean beach, or snuffling for truffles in mature oak forests. 

Pig species are as diverse as their habitat choices. The giant forest hog is well adapted to various forest environments, from swampy thickets to dry savannah woodlands. It can be found in scattered populations across lowland rainforests in West Africa, on the banks of the Congo River and in the mountain forests of Kenya and Ethiopia. Its broad diet, consisting of at least 32 species of plant, allows it to make the most of the foods on offer and adapt to the local climate.¹³

By contrast, the pygmy hog – the smallest wild hog – is endangered, with fewer than 250 individuals in the wild as of 2016.¹⁴ Native to the tall grasslands of north-west Assam in India, the tiny hog has long been near-extinct. Its grassland home, which is also a key habitat for rhinos, tigers and swamp deer, is regularly burned to make way for farmland and new grasses that can be harvested for thatch roofs. A reintroduction programme might be helping to reverse this trend, but with numbers so low, it is hard to prove its success.

Pigs share a lot of similarities with other animals that are considered intelligent, such as corvids (crows and ravens), dogs and monkeys.¹⁵ Evolution has given pigs some smarter senses. The fact that they forage for a wide variety of food, often underground, means they need a few cognitive tools. Pigs also have good memories and will return to places where they have successfully found food in the past.

Pigs have also been shown to be good at laboratory tests, such as mazes, memory tests, simple puzzles and recognising objects. As a result, some researchers consider pigs as quite intelligent. 

Pigs also appear to seek novelty and show playful behaviours. It is thought that this could be the result of having such a varied diet – trying new things and going to new places might benefit an animal that needs to eat a lot of different types of food.

Pigs have highly sensitive snouts that allow them to search for food underground. Roots and tubers make up a significant portion of their diet, and finding these requires a good sense of smell and a sensitive nose that can feel textures in the earth. Their sense of smell is also handy when they are socialising, as it helps them to understand other pigs’ moods. Their vision and hearing are also good, and pigs are able to recognise different humans based on sight and sound alone.

Vietnamese pot-bellied pigs, for example, have been trained to respond to gesture commands – like dogs who are trained to fetch or wait with hand gestures – and retrieve specific objects, such as balls or frisbees, based on gestures. This requires a level of understanding similar to that of dolphins or sea lions.

Other common intelligence tests, such as whether an individual can recognise themselves in a mirror, are inconclusive. However, such tests, which are based on human values of intelligence, are quite contentious within the field of animal psychology.

Featured image © Kenneth Schipper | Unsplash

Fun fact image © Colin Lloyd | Unsplash

1. Barja, Gustavo, and Asunción Herrero. 2000. “Oxidative Damage to Mitochondrial DNA Is Inversely Related to Maximum Life Span in the Heart and Brain of Mammals.” The FASEB Journal 14 (2): 312–18. https://doi.org/10.1096/fasebj.14.2.312.

2. Shull, Caleb. 2013. “Modeling Growth of Pigs Reared to Heavy Weights.” Www.ideals.illinois.edu. May 24, 2013. https://hdl.handle.net/2142/44329.

3. Research), Oliver Keuling (Stiftung Tierärztliche Hochschule Hannover Institute for Wildlife, and Kristin Leus (IUCN SSC Wild Pig Specialist Group). 2018. “IUCN Red List of Threatened Species: Sus Scrofa.” IUCN Red List of Threatened Species. May 8, 2018. https://www.iucnredlist.org/species/41775/44141833.

4. Frantz, Laurent A. F., James Haile, Audrey T. Lin, Amelie Scheu, Christina Geörg, Norbert Benecke, Michelle Alexander, et al. 2019. “Ancient Pigs Reveal a Near-Complete Genomic Turnover Following Their Introduction to Europe.” Proceedings of the National Academy of Sciences 116 (35): 17231–38. https://doi.org/10.1073/pnas.1901169116.

5. Frantz, Laurent A. F., James Haile, Audrey T. Lin, Amelie Scheu, Christina Geörg, Norbert Benecke, Michelle Alexander, et al. 2019. “Ancient Pigs Reveal a Near-Complete Genomic Turnover Following Their Introduction to Europe.” Proceedings of the National Academy of Sciences 116 (35): 17231–38. https://doi.org/10.1073/pnas.1901169116.

6. Jean-Pierre d'Huart, and Rafael Reyna. 2016. “IUCN Red List of Threatened Species: Hylochoerus Meinertzhageni.” IUCN Red List of Threatened Species. January 29, 2016. https://www.iucnredlist.org/species/41769/100471546.

‌7. Jean-Pierre d'Huart, and Rafael Reyna. 2016. “IUCN Red List of Threatened Species: Hylochoerus Meinertzhageni.” IUCN Red List of Threatened Species. January 29, 2016. https://www.iucnredlist.org/species/41769/100471546.

8. Burton, James, Abdul Haris, and Ikeu Sri Rejeki. 2016. “IUCN Red List of Threatened Species: Sus Celebensis.” IUCN Red List of Threatened Species. May 27, 2016. https://www.iucnredlist.org/species/41773/44141588.

9. Burton, James, Abdul Haris, and Ikeu Sri Rejeki. 2016. “IUCN Red List of Threatened Species: Sus Celebensis.” IUCN Red List of Threatened Species. May 27, 2016. https://www.iucnredlist.org/species/41773/44141588.

10. Burton, James, Abdul Haris, and Ikeu Sri Rejeki. 2016. “IUCN Red List of Threatened Species: Sus Celebensis.” IUCN Red List of Threatened Species. May 27, 2016. https://www.iucnredlist.org/species/41773/44141588.

11. Burton, James, Abdul Haris, and Ikeu Sri Rejeki. 2016. “IUCN Red List of Threatened Species: Sus Celebensis.” IUCN Red List of Threatened Species. May 27, 2016. https://www.iucnredlist.org/species/41773/44141588.

12. Research), Oliver Keuling (Stiftung Tierärztliche Hochschule Hannover Institute for Wildlife, and Kristin Leus (IUCN SSC Wild Pig Specialist Group). 2018. “IUCN Red List of Threatened Species: Sus Scrofa.” IUCN Red List of Threatened Species. May 8, 2018. https://www.iucnredlist.org/species/41775/44141833.

13. Jean-Pierre d'Huart, and Rafael Reyna. 2016. “IUCN Red List of Threatened Species: Hylochoerus Meinertzhageni.” IUCN Red List of Threatened Species. January 29, 2016. https://www.iucnredlist.org/species/41769/100471546.

‌14. “The IUCN Red List of Threatened Species.” 2019. IUCN Red List of Threatened Species. 2019. https://www.iucnredlist.org/species/21172/44139115.

‌15. Marino, Lori, and Christina M Colvin. 2019. “Thinking Pigs: A Comparative Review of Cognition, Emotion, and Personality in Sus Domesticus.” International Journal of Comparative Psychology 28 (1). https://escholarship.org/uc/item/8sx4s79c.