The US and Canada could be in line for an explosion in the population of destructive "super-pigs", an expert has claimed.
Jack Mayer, a scientist who has been researching wild pigs for four decades, said that numbers could keep growing rapidly unless there was a major outbreak of swine flu.
There are already thought to be around six million wild pigs in the US. Two million are in Texas while California, Florida and Georgia also have large populations.
Numbers are lower in Canada, where the problem is more recent, but some experts have suggested that pigs could soon outnumber humans in the sparsely-populated province of Saskatchewan.
Mr Mayer told the Daily Beast: "It's a crazy situation with everything that's happened in what I call the Pig Bomb, which has exploded in North America.
"There's not another animal that can put little feet on the ground quicker than a wild pig."
"I've heard it referred to as a feral swine bomb," Dale Nolte, manager of the National Feral Swine Damage Management Program at the U.S. Department of Agriculture, told The Atlantic.
"They multiply so rapidly. To go from a thousand to two thousand, it's not a big deal. But if you've got a million, it doesn't take long to get to four million, then eight million."
The rapid rise in population is thought to have been driven by climate change, which led to higher rates of piglets surviving and more plants growing for pigs to eat.
These "super-pigs" are often wild boar that have bred with other kinds of pig. They are responsible for around $2.5 billion in property damage each year through destroying crops and injuring livestock.
Ryan Brook, a biologist at the University of Saskatchewan, said: "Pig populations are completely out of control.
"The efforts to deal with them are about one per cent of what's currently needed."
Some states like Texas have encouraged people to hunt the pigs, but this is not thought to be a reliable way of controlling the population.
The Canadian province of Ontario and the US state of Montana are both attempting to track the population through collecting data on their movements, with help from the public.
