Previous research on social parasitism has largely ignored allodapine socialparasites, which is surprising given the huge potential of these bees to provide a betterunderstanding of social parasitism. Macrogalea berentyensis, a species that was previouslysuggested to be a social parasite, was collected in nests of M. ellioti, and also in nestsconsisting of only M. berentyensis. These findings, along with morphological and phyloge-netic evidence, show that this species is a facultative social parasite. In the independentlyliving M. berentyensis nests, brood were present that had been reared to an advanced stage,suggesting that: (i) these parasites may be effective at foraging and caring for their brood;or (ii) these nests may be colonies where all the hosts had died, and these parasites had yetto disperse. Macrogalea berentyensis is the closest relative of the facultative social parasite,M. antanosy, and both these species represent the most recent evolutionary origin of socialparasitism within the allodapines. Further behavioral research on both these parasitic specieswould therefore have important implications for the understanding of the evolution of socialparasitism.