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Hi fly-readers,

Yesterday I saw a group (~50-100) of black flies dancing around a dead tree(Dunes/Holland).
They stood still in the air with the (quite long) legs hanging downward.
I couldn't see any difference in these flies, they all looked quite similar.
The flies were black and the wings were very white. Fly-size ~10mm
It could be a group of (only male!) flies of Biblio marci or Biblio hortulanus, the female flies look more different in these species.
Are there fly-species which look similar to this kind of flies or what kind of fly must I think of?
Biblio m. + h. usualy fly from March and April, it is not the time to fly now?

I made a picture of one fly, not a very good one, but you can see some of it.

best regards, Robert