A study of the relationships between 21 southern European, Moroccan and Turkish populations of the Merodon avidus species complex was carried out. Based on a parallel study of type material from several museums, documented diagnostic morphological characters, season of adult activity and geographical distribution, we justify the use of the following names for three closely related taxa in this complex: M. avidus (Rossi, 1790), M. moenium (Wiedemann, 1822), and M. ibericus Vujić nom. n. (new name for M. bicolor Gil Collado, 1930, preoccupied by M. bicolor Walker, 1852). Neotypes of Merodon avidus, M. spinipes (Fabricius, 1794) and M. quadrilineatus Lioy, 1864 are designated. Lectotype of Merodon moenium (Wiedemann in Meigen, 1822) is designated here. A cluster analysis of DNA barcoding sequences clearly separated M. ibericus, but not M. avidus and M. moenium, even though the lack of shared haplotypes, analysis of molecular variance (AMOVA), pairwise Φst values together with allozyme and ecological niche analyses revealed statistically significant percentage of variation among all three species in the Merodon avidus complex. Analysis of 5 diagnostic enzyme loci revealed the presence of genetic differentiation among the M. avidus/moenium complex populations investigated (Fst = 0.654) and species-specific alleles were found at the AAT locus. The presence of two separate related taxa within the M. avidus/moenium complex was further supported by an UPGMA tree based on Nei's (1978) genetic distances. The value of Nei's measure of genetic identity (I = 0.520) between two large (meta) populations of M. avidus and M. moenium suggest that these taxa are sibling species. Populations from Djerdap (Serbia) confirmed the presence of temporal divergence between these species at a locality where they occur sympatrically, while spring and autumn populations from Umag (Croatia) provide an example of morphological plasticity within the species M. avidus. Ecological niche analysis contributed to the species delimitation. Review of the available genetic and ecological data confirmed our hypothesis that the M. avidus species complex, in addition to M. ibericus Vujić nom. n. from the Iberian Peninsula, consists of two sibling species in the rest of Europe and indicated their recent speciation.