Wild Pigs: A Growing Threat in North America
Marcus Lashley is an associate professor of wildlife ecology at the University of Florida.
They go by many names – pigs, hogs, swine, razorbacks – but whatever you call them, wild pigs (Sus scrofa) are one of the most damaging invasive species in North America. They cause millions of dollars in crop damage yearly and harbor dozens of pathogens that threaten humans and pets, as well as meat production systems.
Although wild pigs have been present in North America for centuries, their populations have rapidly expanded over the past several decades. Recent studies estimate that since the 1980s the wild pig population in the United States has nearly tripled and expanded from 18 to 35 states. More recently, they have spread rapidly across Canada, and these populations are threatening to invade the U.S. from the north.
The Super Pigs of Canada
The wild pigs in Canada are unlike any other. These pigs were intentionally crossbred by humans to be larger and more cold-hardy than their feral counterparts in the south. Because of their unique traits, they have earned the nickname "super pigs". In fact, these adults can weigh over 500 pounds, which is twice the size of the largest wild pigs found in many areas of the United States, as shown in a recent study (source).
Understanding the Impact
As a wildlife ecologist, I am fascinated by how wild pigs shape their environment and impact other species. It is crucial to detect and respond to invasive species early on, as it is easier to manage small and localized populations. This is especially true for wild pigs, given their high reproductive rate, ability to expand into new territories, and their adaptability to avoid capture or elimination. Early detection and rapid response are key (source).
Omnivores on the Move
The spread of wild pigs has raised significant concerns, particularly due to the economic damage they cause. Recent estimates suggest that wild pigs cost the United States approximately $2.5 billion annually (source).
A Threat to Wildlife
Wild pigs possess a unique combination of traits that pose challenges for humans. One landowner we spoke with summarized it well: "That makes sense. Pigs eat all the stuff the other wildlife do – they just eat it first, and then they go ahead and eat the wildlife, too. They pretty much eat anything with a calorie in it."
Wild Pigs: Extreme Generalist Foragers
More scientifically, wild pigs are called extreme generalist foragers, which means they can survive on many different foods. A global review of their dietary habits found that plants represent 90% of their diet – primarily agricultural crops, plus the fruits, seeds, leaves, stems and roots of wild plants.
Wild pigs also eat most small animals, along with fungi and invertebrates such as insect larvae, clams and mussels, particularly in places where pigs are not native. For example, a 2019 study reported that wild pigs were digging up eggs laid by endangered loggerhead sea turtles on an island off the coast of South Carolina, reducing the turtles' nesting success to zero in some years.
And these pigs do "just eat it first." They compete for resources that other wildlife need, which can have negative effects on other species.
However, they likely do their most severe damage through predation. Wild pigs kill and eat rodents, deer, birds, snakes, frogs, lizards and salamanders. This probably best explains why colleagues and I found in one study that forest patches with wild pigs had 26% fewer mammal and bird species than similar forest patches without pigs.
This decrease in diversity was similar to that found with other invasive predators. And our findings are consistent with a global analysis showing that invasive mammalian predators that have no natural predators themselves – especially generalist foragers like wild pigs – cause by far the most extinctions.
Altering Ecosystems
There are still many unanswered questions regarding the ecological impacts of wild pigs. It is possible that they indirectly harm other wild species, rather than directly consuming them or depleting their food supply.
Our research has revealed that wild pigs have the ability to alter the behavior of common native wildlife species, including raccoons, squirrels, and deer. Through the use of trail cameras, we observed that when wild pigs were present, other animals adjusted their activity patterns in various ways to avoid them. These behavioral shifts can have significant cascading effects on ecosystems, as they alter the timing and manner in which species interact within the food web.
Another major concern is the potential for wild pigs to spread diseases. They carry numerous pathogens, such as brucellosis and tuberculosis. However, there has been limited ecological research conducted on this issue, and scientists have yet to demonstrate that the increasing abundance of wild pigs leads to a reduction in the population of native wildlife through disease transmission.
Interestingly, in their native range in Europe and Asia, pigs do not cause as much ecological damage. In fact, some studies suggest that they may modify habitats in significant ways for species that have evolved alongside them, such as frogs and salamanders.
Research suggests that feral pigs in North America do not provide any benefits. A review of wild pig impacts mentioned the possibility of generating revenue from selling pig meat or hunting opportunities for landowners dealing with pig problems. Additionally, it is speculated that wild pigs could serve as an alternative food source for endangered large predators or mimic the behavior of locally eradicated or extinct species.
However, the scientific consensus today is that wild pigs are a growing threat to both ecosystems and the economy in North America. The impact of invading super pigs is still unclear, but larger pigs are likely to cause more damage and be better predators and competitors.
While efforts to control wild pigs are already underway in the U.S., the arrival of Canadian super pigs may complicate the situation. Although the idea of invasive super pigs makes for attention-grabbing headlines, their potential effects should not be taken lightly.
This is an updated version of an article originally published on The Conversation on Aug. 26, 2019.
