Rabbits

If you want something to hunt and don't care about the ecosystem, you can learn a lot from Thomas Austin. Austin is the sole reason for the rabbit infestation of Australia.

During the 18 hundreds, Austin, a wealthy man who liked to hunt, moved to Australia. Sadly there wasn't that much around to hunt. Thus he had 24 rabbits brought to Australia. He let a few of them loose hoping for them to repopulate to the point that hunting a few wouldn't hurt. His plan worked.

Austin brought the rabbits back in 1859. Now there are approximately 200 million feral rabbits in Australia.