For more than 20 years, sex allocation in hymenopteran societies has been a major topic in insect sociobiology. A recurring idea was that relatedness asymmetries arising from their haplodiploid sex determination system would lead to various parent–offspring conflicts over optimal reproduction. A possible weakness of existing theory is that only interests of nuclear genes are properly accounted for. Yet, a diversity of maternally transmitted elements manipulate the reproduction of their host in many solitary arthropod groups. The bacterium Wolbachia is a striking example of such a selfish cytoplasmic element, with effects ranging from reproductive incompatibility between host strains, induction of parthenogenesis and feminization of males. This paper reports on a first PCR–based Wolbachia screening in ants. Out of 50 Indo–Australian species, 50% screened positive for an A–group strain. One of these species also harboured a B–group strain in a double infection. Various factors that might explain the unusually high incidence of Wolbachia in ants are discussed. In general, Wolbachia may represent a widespread and previously unrecognized party active in the conflicts of interest within social insect colonies.