Humans have a long history of clever ideas that go horribly wrong. Case in point: the time Australia introduced an invasive species to fight a native species. In 1935, Australia was overrun with the cane grub (aka "greyback cane grub"), a native insect that was devouring Queensland's sugarcane fields. In other countries, the same problem had been solved by introducing cane toads, ravenous toads that could eat the beetles. After some planning, Australians released tens of thousands of cane toads into the fields.
Unfortunately, in Australia, the cane toads didn't do much to combat the grub problem—the sugarcane fields weren't an ideal environment for the toads to live in. Instead, the toads began multiplying exponentially, forcing out native species and creating a much bigger problem on top of the grub issue. Today, they have spread across a substantial portion of the continent, thriving in large part because they're toxic to most predators. Oops.
In 1988, director Mark Lewis released Cane Toads: An Unnatural History, a short, funny documentary on the whole mess. It's a fun watch, and tells the story of the toads from various perspectives—farmers, toad-lovers and -haters, scientists, and even the toads themselves (there are a lot of toad's-eye-view shots). The film is on YouTube in its entirely:
If you enjoyed that, there's a 2010 sequel, Cane Toads: The Conquest, also on YouTube.