From CSULA CS Wiki
It seemed like a good idea at the time. A worker at a Florida dog kennel noticed dozens of snakes living in the rafters and crevices, and decided the reptiles had to go. Working systematically, he killed until none were left.The point is that introducing a mechanism into an environment can have unexpected consequences. So can removing one. In this case removing snake, which is a rat eating mechanism, led to an explosion of the rat population.
Then came the plague of rats.