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Than, what do we have "en somme".
1. Andrey Ozerov with rich field experience confirm that Sepsidae is territorial and he has seen several times that two male show each other wings, than one of them go out, another one left.
2. I (with modest field experience) have seen several times flies from all this families moving wings as well during fiding, in absence of another fly, bieng female.
3. Nobody else know answer so far, as everybody keep silence.