What do ants do when they encounter ants from a different colony?

There are more than 12,500 described ant species to date and many more awaiting description. Each species has a distinct biology. In the majority of cases, an intruder would be killed by the workers of the resident colony.

However, if the intruder is from a colony that is closely related to the new colony, then the workers might not be able to recognize it as foreign and it could sneak in. There are a few ant species, which would accept an ant from a different colony. These ants usually are more primitive in their social organization.  The queen does not take part in the decision process, her job is to lay eggs and to produce pheromones (chemicals), which signalize her dominance over the workers regarding reproduction. The workers perform the task that also involve nest defense against ants from other colonies.