Simulium laciniatum Edwards, 1924 is endemic to Fiji and is also the only known black fly species in the Fiji archipelago, a most unusual situation since neighbouring Vanuatu harbours fourteen precinctive species from the same subgenus, Hebridosimulium Grenier & Rageau, 1961. Morphology indicates that S. (H.) laciniatum is monospecific throughout the Fiji archipelago, so the species was further scrutinised from a molecular standpoint. Samples taken from five islands of Fiji show a major lack of heterogeneity in the mitochondrial COII gene and a probable date around 10⁵ years has been inferred for the S. (H.) laciniatum ancestor, a likely migrant from Vanuatu. COII homogeneity may also reflect the dispersal abilities of blood-seeking females of this species, abetted possibly by shortened distances between islands during ice ages concurrent with depressed sea levels. However, the ITS1 spacer between the 18S and 5.8S rDNA genes exhibits six haplotypes, with the two predominant ones clearly arrayed in a north–south distribution. This suggests sufficient distance between suites of islands in recent times to allow precinctive population development.