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Hey everyone,

we found this insect in the beginning of September in the east-most part of the Alps in Upper Austria, at about 1700m above sea level. It was about 2,5-3cm in size. The silvery shine under the wings appeared to be a kind of air reservoir.

We (3 biology students) observed this insect living under water. In the 30 minutes of our encounter, it spent most of the time resting at the bottom of a ~13 cold nutrient-poor (but with existing fauna) mountain lake. From time to time, it moved to other spots, mostly staying between 20 and 100cm depth.

Based on the habitus, we would've put it in the family of Tabanidae. However, after research, we haven't found any mentions of adult Tabanidae that live aquatic in their adult form. Of course, there are several species with aquatic larvae, but most of them leave the water before pupation.

Does anyone know the species (or correct family if we were mistaken), and maybe more about its way of live?

Thank you,

Gerald