Social parasitism in ants has evolved independently multiple times in various forms.  The parasites successfully infiltrate host colonies, apparently defying nestmate discrimination that safeguards a colony from invasion. Social parasites in the Megalomyrmex genus specialize in attacking fungus-growing ant species, harming the host by draining resources such as brood and fungus-garden.  Megalomyrmex symmetochus, an obligate social parasite, cohabitates with its host completing its lifecycle within the host colony while allowing the host queen to live.  We present the first systematic study observing behaviors between the host Trachymyrmex zeteki and its parasite M. symmetochus.  To document behavioral interactions between host and parasite we videotaped 15 parasitized and 15 unparasitized colonies in the laboratory for 45 minutes each. We also analyzed six experimentally induced infiltrations.  Behaviors between the parasite and host were documented (e.g. indifference after contact, intra and interspecific allogrooming, self-grooming, open-mandible-threat, biting, stinging, antennation, trophallaxis etc.). When a foreign Megalomyrmex ant is introduced into a host colony, the host workers and queen immediately exhibit aggressive behavior.  The parasite will often respond with threatening gaster waves or antennal taps which can cause the assailant to freeze in a defensive posture.  The Trachymyrmex queen aggressively pursues the Megalomyrmex queen which often leads to sting fights.  These assaults do not cease until host ants have received repeated antennal taps from the parasite. During the cohabitation stage host workers extensively clean and investigate the parasite queen; interactions overall appear amiable.  However, the Trachymyrmex queen occasionally harasses the Megalomyrmex queen, even 7 months after infiltration.  This social parasite has the ability to successfully infiltrate and cohabit with the host colony, yet the Megalomyrmex queen is still recognized and not fully accepted into the host colony.