A cross between domestic pigs and wild boars was intentionally bred in Canada. The resulting 'super pigs' escaped captivity and could be invading the US.

• Farmers in Canada cross-bred domestic pigs with wild boars going back to the 1980s.
• When the market collapsed, the "super pigs" escaped and have spread rapidly across the country.
• The environmentally destructive pigs may be invading the US, where feral pigs already pose problems in the South.

A cross between a domestic pig and wild boar was bred in Canada decades ago. After escaping captivity, the "super pigs" spread throughout the country, wreaking havoc on native species and crops.