Ranchers and government officials here are keeping watch on an enemy army gathering to the north, along the border with Canada. The invaders are big, testy, tenacious — and they’ll eat absolutely anything.
Feral pigs are widely considered to be the most destructive invasive species in the United States. They can do remarkable damage to the ecosystem, wrecking crops and hunting animals like birds and amphibians to near extinction.
Wild pigs occupy the “largest global range of any nondomesticated terrestrial mammal on earth,” researchers in Canada recently concluded. They have roamed parts of North America for centuries.
But in recent decades, the pigs have been expanding their range — or more accurately, people have been expanding it for them.
“It’s not natural dispersion,” Dr. Nolte said. “We have every reason to believe they are being moved in the backs of pickup trucks and released to create hunting opportunities.”
In the United States, their stronghold is the South — about half of the nation’s six million feral pigs live in Texas. But in the past 30 years, the hogs have expanded their range to 38 states from 17.
Why the worry? The harm caused by snuffling, gobbling wild hogs is the stuff of legend. The damage in the United States is estimated to be $1.5 billion annually, but likely closer to $2.5 billion, Dr. Nolte said.
“Nature’s rototillers,” experts have said. Feral pigs don’t browse the landscape; they dig out plants by the root, and lots of them. Big hogs can chew up acres of crops in a single night, destroying pastures, tearing out fences, digging up irrigation systems, polluting water supplies.
“Pigs will literally eat anything,” said Dr. Ryan Brook, a professor of animal science at the University of Saskatchewan in Canada.
“They eat ground-nesting birds — eggs and young and adults,” Dr. Brook said. “They eat frogs. They eat salamanders. They are huge on insect larvae. I’ve heard of them taking adult white-tailed deer.”
A recent study found that mammal and bird communities are 26% less diverse in forests where feral pigs are present.
Feral swine have caused extensive damage to cultural and historical sites. The invaders cause $36 million a year in damage to vehicles alone.
“Hitting a two- or three-hundred-pound pig on a highway is not that much different than hitting a two- or three-hundred-pound rock,” Dr. Nolte said. Two F-16 fighter jets have crashed after they hit pigs on the runway.
The swine are also reservoirs for at least 32 diseases, including bovine tuberculosis, brucellosis and leptospirosis. Outbreaks of E. coli in spinach and lettuce have been blamed on feral hogs defecating in farm fields.
In the United States, pig hunting is a popular sport, but biologists caution that it is not always the solution to the nation’s feral pig problem.
In states where populations are not established, hunting creates an incentive for people to distribute feral pigs for sport. Hunting makes the animals warier and scatters sounders, or family groups, which go on to multiply in new family groups.
But where pigs are already well established, hunting can reduce their numbers. Gunning feral pigs from helicopters with semiautomatic weapons is a popular sport in Texas. (There are no hunting seasons for feral swine in the state; the animals, which cause $400 million in crop damage in the state annually, can be shot year round.)
Bottomline – biogas companies are striking arrangements with farmers and agricultural companies to capture and distribute gas from animal waste.