Among samples from 42 colonies of red wood ants that were analysed biometrically 2 were found to represent interspecific hybrids of Formica polyctena FOERST. x F. rufa L. 3 phenotypes (polyctena-like, intermediate, rufa-like) were distinguished in both colonies; their quantitative proportion was almost identical, with predominance of the intermediate forms. The studies were conducted in the Gorce Mts. (the Western Carpathians) from 1985 to 1990.