One of the most controversial ideas in conservation is that of Biocontrol. The goal is to control invasive species or damaging pests by introducing predators/diseases/etc which kill them. Some attempts at biocontrol have been hugely successful. But others have been disastrous, like the introduction of Cane Toads.
Cane Toads (Bufo marinus) were introduced to a lot of places from 1840-1940 to attempt to control agricultural pests.
Now biologists are suggesting that the solution might just be, go figure, biocontrol. But this time they want to use a native species. It turns out Australian Meat Ants (Iridomyrmex purpureus), which are nasty little buggers that kill and eat small animals, could be a solution to the outbreak of Cane Toads. That's because new research has found that the invasive toads are more susceptible to the ants than the native amphibians.
Researchers are hopeful that boosting the ant populations could be a real solution to the Cane Toads. However, they're cautious to endorse such a plan just yet. The ants are generalists, and when given the chance, attack native species at the same rate as the invasive toads. So increasing their numbers could do more harm than good. However, the fact that the Cane Toads are so much more susceptible to attack is promising. More research will focus on how to increase ant populations and how those increases actually affect native fauna. Hopefully, this new biocontrol will far outperform the last one, and won't just backfire, making two problematic biocontrol species instead of one.
UPDATE: Check out a video about this from the National Geographic Channel!
Georgia Ward-Fear, & et al (2009). Maladaptive traits in invasive species: in Australia, cane toads are more vulnerable to predatory ants than are native frogs Functional Ecology DOI: 10.1111/j.1365-2435.2009.01556.x