Villainous, slave-raiding... ants?
The genus of ants Polyergushave evolved to have a very bizarre life-cycle entirely dependent on a second genus of ants, Formica.
A newly hatched Polyergus queen cannot take care of herself, and immediately sets off to find a Formica nest. Once she has found one, she locates, dethrones and kills the colony's queen, and takes command of the Formica (who readily adopt her as their new queen). If the Formica colony is small, the Polyergus queen may wait to kill the Formica queen until a large enough brood is established. The Formica feed, clean and take care of the Polyergus queen, and raise her young for her.
The hatched Polyergus workers are basically useless in the hive, having entirely lost their instincts to take care of themselves, and dependent entirely on the Formica for nearly everything. Without a Formica queen, however, the population of Formica in the hybrid nest (which usually has a ratio of up to 5 slaves per slaver) eventually shrinks as they die off and are not replaced. When the numbers get low enough, Polyergus workers will set off to find a Formica nest and raid it, carrying off pupae and eggs back to their home.
This very complicated and lengthy parasitic relationship between Polyergus and Formica quite often does not work out for the Polyergus, resulting in very few properly established raider colonies. Curiously enough, these raids are also mostly bloodless (save the regicide in queen-killing), and Formica tend to just move to the side and wait for the raid to end instead of getting involved. Scientists are also trying to encourage human cultural models other than slave-raiding to explain the life-cycle of Polyergus, such as referring to Polyergus as pirates or Formica as "helper-ants" or domesticated animals.
Word of the Day - "Spoilate" : to rob, plunder or despoil