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Multiple evidence is presented that Myrmica constricta Karavajev, 1934 represents a cryptic sister species (= sibling species) of Myrmica hellenica Finzi, 1926: (a) males differ significantly in length of appendage pilosity, relative scape length and absolute body size; (b) a discriminant analysis (DA) and a leave-one-out-cross-validation discriminant analysis (LOOCV-DA) using 14 morphometric characters separated 90 worker nest samples of both species with a predicted error rate of 1.1 %; (c) as unsupervised method, a principal component analysis of the same data set fully confirmed this clustering; (d) Mantel tests showed a significant effect of the hypothesised con- vs. heterospecificity based on the morphological distance (OMD) as well as on the Bray-Curtis similarity index (BCSI) of worker nest samples, also when controlling for geographical distance (OMD: partial correlation r = 0.3480, p < 0.01; BCSI: r = –0.3254, p < 0.01) and hence provide a further independent argument for heterospecificity. A DA and a LOOCV-DA clearly allocated the types of M. hellenica (with p = 1.000 and p = 0.981, respectively), M. rugulosoides var. striata Finzi, 1926 (in both analyses with p = 1.000) and M. rugulosa var. rugulososcabrinodis Karavajev, 1929 (both with p = 1.000) to the M. hellenica cluster and the types of M. constricta (both with p = 1.000) to the M. constricta cluster. Hence, M. striata and M. rugulososcabrinodis are demonstrated as junior synonyms of M. hellenica. Myrmica constricta is a more western and northern species and goes north to 60°N while the Ponto-Caucasian M. hellenica does not pass 46°N. The species are sympatric in Italy and the Balkans and there are no clear suggestions for hybridisation in this area. A distribution map, comparative morphometric tables and drawings of both species are presented as well as data on colony structure, habitat selection and behaviour of M. constricta.