Abstract: A taxonomically problematic ant species from southernmost Finland, so far determined as Formica rufibarbis Fabricius, 1793 or / and F. cunicularia Latreille, 1798, is identified as Formica lusatica Seifert, 1997. This is the first report of this species from Finland. Aspects of the biology of F. lusatica under the local conditions, and especially its relations with Formica sanguinea Latreille, 1798, are presented and the description of its males is given.