Rabbits

After their introduction into Australia in 1859, rabbits became an ecological disaster, a plague of almost Biblical proportions. A series of articles, not for the squeamish, by Karl Kruszelnicki gives some background (part 1, part 2, part 3).

The same thing happened in ancient Carpathus (or Karpathos, modern Scarpanto), an island about 30 miles southwest of Rhodes in the Mediterranean Sea:

• Aristotle, Rhetoric 3.11.14 (tr. John Henry Freese): If a man, for instance, introduces into his house something from which he expects to benefit, but afterwards finds himself injured instead, it is as the Carpathian says of the hare; for both have experienced the same misfortunes.
  
• Hesychius (tr. J.M. Edmonds), commenting on Archilochus fragment 248 West: A proverb in the form 'the man of Carpathus the hare,' supply 'introduced'; there being no hares on the island, the people introduced them, and they became so numerous that their corn and vines were damaged.
  
• Suda (tr. David Whitehead): They say that the Karpathians, being islanders, brought in a hare, because they did not have [any] in their territory. But the hares became numerous and ruined their agriculture. So the proverb is applied to those devising something to their own detriment.