The results of laboratory experiments carried out with both monogynous and polygynous colonies of the formicid Messor barbarus (which under natural conditions are always monogynous) showed that workers belonging to monogynous colonies were able to discriminate between intruders from other monogynous colonies and those from polygynous (di- and trigynous) colonies. Since differences in the relative proportions of the hydrocarbons carried are known to convey complex messages that are used for recognition purposes, experiments were conducted to determine if any differences existed in the proportions of the various hydrocarbons carried by diverse categories of intruders. It emerged that one set of hydrocarbons, which were usually present in rather small proportions and included all the families that constituted this species' chemical signature (n-alkanes, mono-, di- and trimethylalkanes), was characteristically associated with workers from monogynous colonies. Another set of hydrocarbons, which included some of the above components, mostly in larger relative proportions, could be said to characterize the digynous and trigynous colonies.