13. Overrunning Australia
Hares and rabbits are not native to Australia. Thus, there were no native predators Down Under that had evolved to feed on and keep their numbers in check. So from cute and cuddly and sometimes delicious animals, hares and rabbits morphed in Australia into feral and invasive pests that devastated much of their new home.
As early as the 1820s, settlers were complaining of rabbits overrunning the place. By the 1860s, between the disappearance of many natural predators, mild seasons allowing for year-round breeding, and natural selection producing a hardier breed of wild rabbits, their population exploded.