Morphological analyses of female wasps collected at different points in the development of the colonial life cycle showed that inPolybia occidentalis,P. paulistaandP. scutellaris, caste differences progressively increase because larger queens appeared in more abundance in later stages of the colony cycle. Possibly, the mechanism can be of selective importance in the onset of the cyclical oligogyny, which is presently well documented in the life cycle of many swarm-founding polistine wasps. Males and uninseminated females with developed ovaries (intermediates) only occurred at the later stages of a colony’s developmental cycle.