Slave_making ants Polyergus breviceps invade nest of Formica gnava in search of their unborn brood. Slave_making ants have lost the ability to take care of themselves and their young, and must enslave other ants to perform those functions. They will take the brood back to their own colony where they will serve as slaves. Slave_making ants are about 6 mm in length and are common in the southwestern U.S.