Think about the the worst invasive species you know. Kudzu: smothering trees and houses, growing one foot per day. Burmese pythons: stripping the Everglades of small animals. Asian carp: streams cleared of plankton and swimming towards the Great Lakes.
They all came from elsewhere, arrived without natural predators, supplanted local flora and fauna, and invaded entire ecosystems. But they all have their limitations: kudzu dies in a hard freeze, carp can’t stand salt water, and pythons can’t travel long distances very quickly. (Fortunately.)
Now imagine a species with all these advantages – foreign origin, no enemies – and no obstacles to dominance: a species indifferent to temperature, at home in many landscapes, able to run much faster than you and sufficiently muscle to leave a big dent in your car. This describes one of the 6 million feral pigs in the United States, the most intractable invasive species that most people have never heard of.
“If you wanted to create the perfect invasive species, a species that could live just about anywhere, eat anything, have a very high reproductive rate, be extremely destructive and also very difficult to control, you You wouldn’t have to look any further than the feral pig,” says John “Jack” Mayer, technical program manager at the Federal National Laboratory in Savannah River in South Carolina, and a recognized authority on feral pigs. “They can live just about anywhere, from the frozen provinces of the Canadian Prairies to the hot, humid deserts of the American Southwest and everything in between. They are the ultimate survivor.
Feral hogs – or feral pigs, boars, feral hogs, or razorbacks – are not new to the United States; by some accounts, they arrived in the 1500s, shipped by Spanish colonizers as a mobile source of meat. Over the centuries, they settled in the forests of the southeastern United States, intermingling their genes with those of escaped domestic pigs and Eurasian boars imported for hunting. This ad hoc cross produced a 3-foot-tall, 5-foot-long pack of tusks and razor hairs that retains the aggressiveness of its wild ancestors while possessing the large litters and rapid reproductive cycles of domestic pigs.
Which might have been good, if the pigs had stayed in the forests. But over the past few decades, they’ve moved: through suburbs and into cities, at one point reaching 48 states. To a wild pig, modern human landscapes – agricultural fields, flower gardens, golf courses, dumps – are all-you-can-eat buffets. “Anything that has a calorie, they eat,” says James LaCour, the state wildlife veterinarian with the Louisiana Department of Wildlife and Fisheries. “It’s a mammalian cockroach.”
The inherent challenge of feral pigs is not just the damage they cause, although this is estimated at $2.5 billion per year. Nor are they diseases they can transmit to domestic pigs or humans, although the dire possibilities keep biologists awake at night. It’s just that there’s no way to control them. Fences cannot hold them back. Trapping and shooting can only reduce their numbers when populations start small. And despite abundant research, pharmaceutical controls – whether contraceptives or poisons, what biologists call toxins – are still a few years away.