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Hi Nikita,

Yesterday I studied a specimen from Finland which looked similar to the one on your picture. The abdomen had the banded patern which you typically find in females of Geomyza balachowskyi.However, since the marking on the tip of the wing was rather extensive, I had my doubts about the specimen being G. balachowskyi. After treating the tip of the abdomen with a 10% KOH solution, I studied sternite 8. The specimen turned out to belong to G. hackmani Nartshuk, 1984 without doubt.
The marking on the tip of the wing in your specimen also seems to be rather extensive. Furthermore in the Moscow region G. hackmani is probably much more common than G. balachowskyi. So I hereby let you know that it is more likely that your specimen belong to G. hackmani than to G. balachowskyi.
My apologies for the confusion!

By the way, the "gymnastic wing moving" is a behaviour I have seen frequently in both Geomyza tripunctata and G. balachowskyi (the two species of the genus Geomyza I most commonly find in The Netherlands).

Jan Willem