The objectives of this study were to analyse the diversity and geographical distribution of the blackfly species from the Huebra River basin located in Salamanca province, Western Spain. This research significantly contributes to expanding our knowledge of the Simuliidae family. The study not only increases and ameliorates faunal and bioecological data, but also enhances the understanding of blackfly species across the Spanish national territory. The identification of 23 species has led to the addition of six new records to the simuliid fauna of the region: Simulium (Nevermannia) armoricanum Doby & David, 1961; Simulium (Nevermannia) carthusiense Grenier & Dorier, 1959; Simulium (Nevermannia) naturale Davies, 1966; Simulium (Nevermannia) vernum Macquart, 1826; Simulium (Simulium) bezzii (Corti, 1914) and Urosimulium faurei (Bernard, Grenier & Bailly-Choumara, 1972), expanding the previously recorded 19 species to 25. This study also provides valuable insights into the biology and geographical distribution of these species. It sheds light on the ranges of altitude, water velocity, temperature and the depth of watercourses conducive to preimaginal development. Additionally, it offers new information on the abundance of larvae and pupae, revealing the diverse ecological gradients that influence their occurrence and distribution patterns. The results indicate that the diversity of blackfly species varies according to factors such as altitude, water velocity, turbidity, and water temperature.