When Pigs Run Wild ..... Bad Things Happen

Sus scrofa is the scientific name for wild boar, wild hog, feral pig, feral hog,  razorbacks and several other common names used to describe this species. It also include domestic/farmed pigs. It does not include peccaries/javalinas, bushpigs, babirusas or warthogs.

It is one of the most widely distributed large mammal species in the world, existing on all continents except Antarctica. They are native to Eurasia and parts of North Africa.

The Misplaced

Appearance

There is a lot of body variation in this species as they are so widespread and subject to so many different physical conditions. Also a variety of subspecies exist and there have been numerous natural and artificial cross breeding events over millenia of pig meets pig.

Length range: 150 - 240 cm

Weight range: 70 - 270 kg

Colour range: One solid colour or spotted, variety of colours including white, black, brown, tan

Breeding

Males are considered to be sexually mature at about 6 months and females at about 10 months, although they seldom breed successfully at such young ages.

Litters usually consist of between 3 and 12 young and females generally produce one or two litters per year throughout their reproductive lives. The gestation period varies between 100 and 140 days.  At birth, the babies may have longitudinal stripes in their coats  which disappear as they mature. It is thought to aid in camouflaging the vulnerable piglets. Young are weaned in 3-4 months, often depending on when the next litter arrives.  Early mortality rates can be as high as 60%.

Longevity of wild pigs is thought to be between 5 and 15 years. Estimates vary.

Ecology

Due to their inability to sweat, pigs need to have access to wet soil to wallow to regulate temperature, so, they do not invade desert areas. There are dissenting opinions about wild boars invading areas with significant snowfall.¹ ,²

Pigs are omnivorous, and are opportunistic and adaptable in their diets. They  feed by using their their tusks and snouts to root through the ground in search of roots, tubers, bulbs, worms, insects, slugs and snails, nuts, as well as frogs, lizards and snakes, rodents and other vulnerable mammals such as young fawns.  They are also known to consume bird eggs, nestlings and burrowing adult birds.

Their predators include big cats such as bobcats and jaguars, some of the larger birds of prey, foxes, feral dogs, bears. Predation is more likely in the juvenile stage as many more predators are able to deal with a juvenile than a fully grown adult specimen.

Wild boars are host to a number of parasites including worms, nematodes, and act as disease vectors for leptospirosis, toxoplasmosis, brucellosis, swine influenza, salmonella, hepatitis, and pathogenic E. coli

The Displaced

Particular species are not directly targeted by the invasion of wild boars. They change conditions in many aspects of the novel ecosystem, and therefore they displace multiple species when they invade.

The mechanisms of displacement include

• habitat alteration e.g. destruction of  riverbanks, removal of ground cover
• competition e.g. they compete with many species as they hog 🙂 food sources
• predation e.g. because the pigs diet is so broad, they act as predators of many animal species
• disease spread e.g. S. scrofa carries viruses which can have a devastating effect on native species

The Consequences

Where is the invasion?

Sus scrofa is recorded as introduced in 75 countries or islands. Wild pigs have been documented as a threat to 672 taxa from 54 different countries.

Some examples of the effects of invasion by wild boar

According to University of Hawai'i ecologist, Derek Risch,

Wild pigs are unique among other species since they are herbivores, top predators, and ecosystem engineers, modifying ecosystems by digging and rooting. We found that in addition to the over 300 plant species threatened by wild pigs globally, wild pigs actively predate and destroy critical nesting sites for hundreds of threatened and endangered reptiles, amphibians and birds.³

Hawai'i

Hawai'i has a feral pig problem. Feral pigs have endangered many of the native plant species by overgrazing in the rain forest. They churn up the forest floor in search of earthworms and fleshy plant roots and destroy vulnerable native plants such as mints and orchids. The starchy core of native tree ferns is also among the pigs' favorite foods. The pigs rip the bark of trees which can lead to their death. Opportunistic plant species, often also invaders, may occupy the habitats remaining after feral pigs have eliminated native species. Seeds of invasive plants can be transported by being carried on pigs' coats or scattered in their faeces thus allowing them to gain a  a new foothold in the forest, Also the hollows the pigs make in mud and disturbed trunks provide increased real estate for mosquitoes to breed and spread disease.

Australia

Pigs were introduced into Australia with the first European settlers in 1788. By the end of the 18th century, they were already regarded as a nuisance as they destroyed crops and trampled pastures.
Guesstimates of current wild pig numbers in Australia have ranged from 3.5. million to 23.5 million. They are found in all states.

According to The National Feral Pig Action Plan published in 2020,

In 2013, the Threat Abatement Advice (TAA) identified 161 species of threatened flora and fauna at a national level as being adversely affected by feral pigs. However, the TAA only included species that are federally listed under the Environment Protection and Biodiversity Conservation Act (1999).
There are 442 state listed threatened fauna species impacted by feral pigs, 55 of which are dependent on a specific vegetation structure or lay their eggs in the soil and are at risk of feral pig activity. Similarly, there are 2,319 state listed threatened flora species that are considered likely to be at risk from feral pigs, particularly where they occur in regions frequented by pigs.⁴

Eradication strategies

Poisoning by baiting

This is probably the most popular method of eradication. It can have the disadvantage of accidentally killing other species, but newer techniques are being developed to target wild pigs very specifically.

Trapping and Snaring

Trapping is another strategy that has been tried to control wild pig numbers. It is relatively expensive in terms of time and money, and only suited to small numbers of animals. Snaring has also been tried.

Aerial shooting

Aerial shooting has been found to be more useful in most situations rather than shooting at ground level.

More methods are under development

Note

Unlike the situation of most other invasive animals, there are certain groups of people who resist the erasure of wild pig populations.  Business which sell pig-hunting experiences and groups which utilise wild boar products such as food items and pelts have reservations about the level of control that some government programs have sought to exercise over hog numbers.

The collective name for a group of wild pigs is a sounder.

Some wild pigs living in areas favourable to their survival have weighed in at more than 350 kg. Domestic pigs who don't need to forage and are fed premium diets  can reach weights of over 1000 kg.

Dig Deeper

• The global impact of wild pigs (Sus scrofa) on terrestrial biodiversity
• Threat abatement plan for predation, habitat degradation, competition and disease transmission by feral pigs
• Feral pigs are ruining ecosystems across 35 states and hunting is making it worse
• Assessing feral swine damage in the western gulf region of Arkansas, Louisiana, and Texas