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The title is explicit.
Tiny (2 - mm) black, active flies all over a window yesterday.
Same thing to-day.
As the weather was warm, we had other windows open, and it is not clear to me where from the swarm originated (indoors ? outdoor ?).

Identification suggestions ?

Pictures were kept large for details to be visible, but they are strongly compressed not to be a nuisance on loading.







Many thanks to our experts.

Dimitri