The Mediterranean basin is a region of species richness, rarity and endemism, and is thus an area of significant conservation importance. Conservation of insect biodiversity benefits pollination services in the fragmented Mediterranean landscape. However, the question of the distribution patterns of an important long-distance pollen disperser, the hoverfly Eristalis tenax (Diptera, Syrphidae), remains open. Therefore, we explored the spatial distribution of genetic and phenotypic diversity of this species across the Central-Eastern Mediterranean. Connectivity between continental and island populations of E. tenax was studied by integrating molecular (allozyme loci and mitochondrial DNA sequences of the cytochrome c oxidase subunit I gene) and phenotypic data (wing geometric morphometrics). Allozyme (FST values, STRUCTURE analysis, analysis of molecular variance) and phenotypic data (wing shape) and landscape genetics (Alleles in Space analysis) suggest that E. tenax populations within the Mediterranean are largely connected, and that there is an absence of large-scale geographic structuring. Intraspecific variability was only 1.54% among samples, and the Mediterranean populations showed an almost complete lack of COI mtDNA haplotype diversity. Thus, our results suggest that E. tenax populations are well mixed, and that a considerable amount of gene flow takes place, even among populations that are a great distance apart. As E. tenax's ecological amplitude is wide, and the species is therefore widespread in both natural and man-made landscapes, it probably maintains a high level of population similarity by its large population sizes (as revealed by the θ parameter) and constant intermixing among populations. From an applied point of view, large-scale species intermixing enables pollen spread across distant island plant populations, especially those threatened by extinction.