There are around 15,000 discovered ant species in the world as of 2015, 50 of them show slave-making behavior. Ants are social insects, using mainly pheromones to communicate to one another. Much like the immune system, the most important communication is determining self and non-self. In the case of ants, colony member or non-colony member. Members of colonies have particular scents or pheromones that identify them. The communication pheromones are produced in the Dufour’s gland which has a variety of functions in the class hymenoptera, to which ants belong (along with bees, wasps, and saw-flies).
The photo shows the large parasitic queen ant, Polyergus lucidus with its host species Formica archboldi.
There are two mechanisms in which ants are made into slaves. One is brood theft, which involves the slave-making ants stealing pupae from other colonies. Thieving behavior is seen all across the animal kingdom, one extreme example being kleptoparasitism.
Nylanderia fulva worker with pupae. This species is not related to slave-making species, but is a good picture of pupae.
Then, there are ants whose queen is inserted into the nest of another ant colony and takes over as queen. This is done by killing the actual queen and mimicking her pheromones making the other colony ants believe that she is their queen. The ants of the host colony then groom her and take care of her as if she was their own queen. The host ant colony also helps take care of the slave-making queen’s offspring.
In other cases the slave-making colony and another colony have a full on battle where, if the slave-makers succeed, the adults of the host colony are killed. During the battles the slave-makers use a type of chemical warfare, secreting hormones from the Dufour’s gland that cause the host colony to attack itself. The pupae of the host colony are exposed to pheromone to make the host ants believe the slave-making queen is their queen.
Often, once a slave-maker colony has colonized the host habitat, the workers of the slave-maker species and some of the host ants will leave the colony to get more slaves. This often results in ants of the host species helping to enslave those of their species.
In areas where slave-making ants are present, the host ants are extremely aggressive toward the parasitic ants. The aggressive actions aimed to kill and or, more often, immobilize the brood thief. Anti-theft behaviors can vary depending on the tactic being used by the brood thief.