Phylogeny

How did this all start?

A hundred years ago, an Italian myrmecologist named Carlo Emery noticed that many of the parasitic enslaver species closely resembled their preferred host species. Since then, it's been confirmed that most parasite/host pairs are closely related. This is based on the fact that it's far more likely for a stolen larvae of a closely related host species to be fooled by a closely related enslaver species to work normally than by an enslaver species that looks and smells drastically different. This is now referred to as Emery's Rule, and has been generalized to many non-ant species.

In order for a slave making species to keep slaves, the slave makers rely on the slaves not realizing they belong to a different species.

There are two potential causes for Emery's observation.

We start with a species of ant. It becomes reproductively isolated through some mechanism, geographic, temporal, or otherwise. Once the speciation occurs, individual ants sometimes recognize their related species as members of their own colony because they still share many of the same pheromones. This is an exploitable mistake.

The other cause could have been through a particular series of events during a territorial war between two colonies of the same species. Ants regularly fight for territory and it is An ant of one species, if placed in another species colony will continue to carry out its duties just as it would if it were in it's own colony because it is unaware of the situation. This is only possible because the to be enslaver species does not smell drastically different or conduct it's goings-on in a largely different manner.