Although the biology of most genera of allodapine bees is relatively well known, there are only fragmentary data on one African species of a basal genus, Halterapis, and there have been no studies of this genus from Madagascar where it is most speciose. We present the first account of nesting and social biology of a Malagasy species in this genus, Halterapis minutaBrooks & Pauly, based on a sample of 23 nests This species has a unique form of brood provisioning, where a clutch of eggs is mass provisioned with a single, long cylindrical pollen mass, and larvae gradually eat their way along this food store. Most colonies contained more than one adult female, with generational overlap and very strong size-related ovarian differentiation among nestmates, indicating that the species is eusocial. Sex allocation was extremely female biased, and this is probably linked to reproductive skew within colonies. Our findings indicate that the lack of true sociality in the African species Halterapis nigrinervis (Cameron) is apomorphic and not linked to mass provisioning per se, although it may be linked to mass provisioning of individual eggs. The form of sociality in H. minuta emphasizes earlier findings that sociality is frequently very complex in allodapine bees and further indicates that extant members of the tribe Allodapini do not represent early steps in the origin of eusociality.