Insect societies are normally closed entities from which alien individuals are excluded. The occasional fusion of unrelated colonies of the thelytokous ant Platythyrea punctata is therefore puzzling, because it strongly intensifies competition among nestmates for the replacement of an old reproductive. Most colonies of P. punctata have only one or few reproductives, which produce female offspring from unfertilized eggs, and therefore have a clonal structure. Fusion leads to multi-clone colonies. We compared the occurrence of dominance and policing behavior between single- and double-clone colonies. We find that the frequency of aggression is higher in double-clone colonies, but that individuals do not preferentially direct attacks toward non-clonemates. This matches observations in other species that social insects perceive genetic homogeneity but are not capable of reliable discrimination among nestmates of different degree of relatedness.