A description of the male adults of fiveChaetocladiuss. str. species (C. castellaesp. n.,C. lencioniaesp. n.,C. lodscrozetaesp. n.,C. macunensissp. n. andC. muttensissp. n.) is provided based on material collected in some glacial alpine springs and cold streams located in the Swiss Alps (altitude 1800–2700 m). Male adult of the nearestChaetocladiusspecies known from Europe and neighbouring areas belong to:C. aedeagolobatusRossaro, Magoga & Montagna, 2017;C. insolitusCaspers, 1987;C. gracilisBrundin 1956;C. antipovaeMakarchenko & Makarchenko, 2011;C. dissipatus(Edwards, 1929),C. holmgreni(Jacobson, 1998),C. egorychMakarchenko & Makarchenko, 2017. Although some resemblance can be found between the five diagnosed and described species and other related members of theChaetocladiusgenus, the taxonomic position cannot be clarified until current comprehensive work on the genus is complete. Geographical distribution of the five new species is currently restricted to the two Alpine Swiss glacial catchments: upper basins of the Rhône River and Muttbach streams; streams and lakes delimited by the Macun area. This highlights the importance of some high mountain ranges, considered as cold glacial enclaves and hotspots of endemism, in the preservation and persistence of autochthonous alpine relic species. Such species are considered as relevant biogeographic representative and their loss would be biologically indicative of global warming and climate change. Currently, there are only seven recordedChaetocladiusspecies from Switzerland:C. coppaiMoubayed-Breil, 2017;C. laminatusBrundin, 1947; C. cf. longivirgatus Stur & Spies, 2011;C. melaleucus(Meigen, 1818);C. perennis(Meigen, 1830);C. piger(Goetghebuer, 1913);C. suecicus(Kieffer, 1916). Consequently, the description of the five new species increases the total number in the genusChaetocladiusto twelve for this country. Remarks and comments on the taxonomic position, ecology and geographical distribution of the new described species, with key to known male adults from the upper catchment of Rhône River (including Muttbach valley) are provided..
