The results of the study of the variability of Formica lugubris Zett. in the Baikal region were shown. We found a phenotypic differentiation of populations of ants. There are three groups of ant's populations differing on color patterns. The darker Pn 4 morph prevails in the western and eastern groups and the brighter Pn 3 morph prevails in the central group. It is possible that these three groups of populations of ants colonized this region from different local postglacial refugia. Earlier, the similar pattern of variability has been discovered for Formica aquilonia Yarr. in the Baikal region.