Endemic black flies in Switzerland? A taxonomic issue

Endemic species have special significance in matters of biodiversity and conservation. Their limited distributions make them especially vulnerable to local and global threats such as climate change, landscape modification, and invasive species. The job of taxonomists is to reveal species, define their taxonomic limits, and provide unequivocal means of identifying them. For entities that were named and described as species in the early years of biological classification, the task can be challenging. We examined two species described more than 180 years ago, both putatively endemic to Switzerland: Simulium lividum (Schellenberg, 1803) and Simulium canescens Bremi, 1842. Switzerland is a small, mountainous country of about 41,000 square kilometers, ranking as the world's 135th largest country, with a mean elevation of about 1,350 m and about 4.3% of its area covered by freshwater (CIA World Factbook 2025). Although the country has a rich insect fauna, with estimates of up to 60,000 species (Widmer 2021), it is not known for its endemicity. Only a limited number of species are considered endemic, such as a few species of ants (Social Insects Specialist Group 1996). Switzerland was almost entirely covered with ice during the Last Glacial Period up until about 19,000 years ago (Leesch et al. 2012), making it unlikely that endemic species would be found in the country today. Although both names, lividum and canescens, have appeared in modern world catalogues of the Simuliidae (Smart 1945, Adler 2025), both have been ignored in comprehensive treatments of the Palearctic fauna (e.g., Rubtsov 1959-1964) and in previous treatments of the simuliids of Switzerland (Glattaaar 1998). Crosskey (1988) considered both names to be nomina dubia but later listed them as 'Simulium sensu lato species unplaced to subgenus' (Crosskey & Howard 1997) where they have remained (Adler 2025). However, S. lividum was considered a nomen dubium and removed from the checklist of Diptera of Switzerland, whereas S. canescens remains a valid species among the 35 simuliids listed for Switzerland (López-Peña 2024). We maintain that it is counterproductive to continue recognizing S. lividum and S. canescens as endemics of Switzerland or to continue recognizing them as unplaced species unable to be identified by specialists. We, therefore, provide a rationale for redressing the matter.