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Five years' data on phenology of an Anthidium manicatum population in southern Germany and comparative observations on A. manicatum and A. florentinum from southern France are analysed. Males and females had the same flight season, adult sex ratio was strongly female biased and males were larger than females in both species. This is the opposite pattern to most other solitary bees, where females generally are larger than males, sex ratio is male-biased, males emerge before females and males disappear long before females. We argue that two features of Anthidium female behaviour, namely prolonged sexual receptivity and use of resources easily defendable by males, explain male adaptations in behaviour, phenology and body size and, hence, population sex ratio.