The nanus group of the genus Merodon Meigen (Diptera, Syrphidae) is revised, yielding an illustrated key, a discussion of taxonomic characters and morphological diagnosis for the five species of this group. Three new cryptic species are described, Merodon kopensis Vujic et Hayat sp. n., M. neonanus Vujic et Taylor sp. n. and M. rasicus Vujic et Radenkovic sp. n. New diagnostic characters are given for M. nanus Sack and M. telmateia Hurkmans. In addition, environmental profiles for each investigated species have been defined and compared, and maps of distribution and richness created. Niche dissimilarity was found for each species. Eastern Anatolia and the southern Aegean region of Turkey are reported as the most species rich regions for the nanus group.