They attack other colonies, plunder and rob, kill other colonies' inhabitants or keep them as slaves: Ants are usually regarded as prototypes of social beings that are prepared to sacrifice their lives for their community, but they can also display extremely aggressive behavior towards other nests. Evolutionary biologists in Germany have found that ant colonies are more productive and raise more offspring when the workers in the colony display considerable variation in their levels of aggression. This variation in aggression is possibly part of their division of labor, which is regarded as the basis of the success of social insect societies.

Source: Ant colonies: Behavioral variability wins