Mother-offspring analyses were carried out in three species of Formica ants in order to estimate the frequency of multiple mating and to test for randomness of mating. The mating types deduced on the basis of genotypic data agreed with the assumption of random mating in F. sanguine a and F. transkau-casica, whereas those in F. pressilabris departed from randomness. The results suggest that F. trans-kaucasica can be considered chiefly monoandrous. F. pressilabris shows a moderate frequency of double matings, and F. sanguinea females commonly mate with at least two males.