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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

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Dear Plusko

Yes, this is a horsefly (Tabanidae) not doubt.
But your text confuses me. This picture clearly shows a female horsefly on the ground, hence, above water. And staying at 100 cm below water level ? That would be very difficult to observe.
So, I am misunderstanding your text ? Could you please elaborate ?

Thanks


Theo

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No, you understood correctly.
The picture was taken when it was around 40cm below the water surface.

It was a crystal clear lake, that's why the only trace of the water in the picture is that it's a little blurry.

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Thanks for the confirmation. This would be very impossible in dutch waters, hence my question.
Adult Tabanids are not aquatic insects. This is the first report known to me of such behavior. It also makes little sense to me. My best guess that we are looking at the result of some kind of accident and / or dying female. Being in very cold water would make it impossible to function normally. The white spots on the wing might be drops of air, but they are definitely not used for breathing, if that would be suggested.

First time for everything, I guess !

Theo