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Abstract: Queen polymorphism, the coexistence of two or more phenotypes of reproductive females in one species, is an uncommon feature in ants. In several ant species, queen polymorphism turned out to be genetically mediated. Monomorium cf. rubriceps Mayr, 1876 from south-eastern Australia is another species with workerlike, intermorphic queens but also alate / dealate ordinary gynomorphs. However, field and laboratory experiences suggest that this polymorphism is environmentally determined, in that a functional intermorphic queen inhibits the formation of alate gynomorphs in her progeny. Such gynes develop from her remaining brood when the queen has been removed or has died. Details of collecting sites, colony size and composition, reproductive organs and of the morphology of the reproductives are presented here. The author recommends further investigation of the phenomenon.