The social wasps belong to three monophyletic vespid subfamilies, Stenogastrinae, Polistinae and Vespinae. They have been considered as key groups to understanding the evolution of social behavior in insects. They also provide us suitable material for making good progress in the field of natural history. One reason for this could be the fact that the current species-level classification of social wasps are more or less well established, allowing us to carry out to revise the classification based on the taxonomic practices, such as comparative study with a modern species concept. In this paper, I present the summaries of two subjects. The first is about a hover wasp genus, Eustenogaster, and the wasps of this genus have bivoltine life cycle. The second treats speciation and dispersal of Polistes japonicus species-complex in the Nansei Islands.