Although parental care has been studied primarily in vertebrates, invertebrate parental care strategies are incredibly diverse, ranging from simple egg-guarding to the most complex eusocial societies. We are using experimental and phylogenetically-controlled comparative approaches to investigate the evolution of parental care strategies in apoid wasps. For example, we are interested inthe evolution and ecology of progressive provisioning, which is often regarded as a 'preadaptation' for the evolution of eusociality. In progressively provisioning wasps, as in many vertebrates, offspring are given food only gradually as required, instead of receiving a single large mass of food at the time of oviposition (the ancestral condition).