From that engine of nightmares National Geographic:
In South America female phorid flies have developed a bizarre reproductive strategy: They hover over fire ants, then inject their eggs into the ants with a needle-like appendage.
The egg grows and the resulting larva generally migrates to the ant's head. The larva lives there for weeks--slurping up the brain and turning the ant into a "zombie," in some cases compelling the ant to march 55 yards (50 meters) away from its colony to avoid attack by other fire ants.
Finally the baby fly decapitates its host and hatches, exiting through the ant's head.