It has been hypothesised that single mating (monandry) by females is a primitive characteristic in eusocial Hymenoptera, and that evolution of mating systems generally proceeds from monandry to polyandry. Rigorous testing of this hypothesis requires both a reliable phylogeny, and mating system characterisation by genetic markers for the study taxa. This hypothesis was tested in the ant genus Lasius. Average queen mating frequency was characterised by microsatellite markers for 6 species (L. niger, L. psammophilus, L. neglectus, L. umbratus, L. carniolicus, L. fuliginosus) representing four different subgenera. The species-level characteristic queen mating frequencies were mapped into the phylogeny of Lasius (provided by courtesy of Riitta Savolainen, University of Helsinki). The results so far indicate that multiple mating within Lasius is confined to one clade.