The Colletes fasciatus-group is endemic to the winter rainfall area of western South Africa and comprises about 35 species with 11 of them having reduced female scopae. These species very probably carry pollen for nest provision in their crop. Two stages of scopa reduction can be distinguished possibly representing consecutive steps towards a total loss of specialized hairs on the hind legs. Microscopical analysis of pollen collected by females of species with developed scopae and a review of published data revealed a strong preference for Aizoaceae that have small to very small pollen grains. A hypothetical scenario for the evolution of scopa reduction is discussed based on flower preferences and considering the harsh environmental conditions during the flowering season in winter and early spring.