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very interesting photo indeed. I think that Calliphoridae is correct but I don't recognize the species. I haven't met every genus and species. Did you collect these? do you have other photos? I cannot see enough details to even identify a genus. I think that Calliphora is not possible based upon the wing alone. Onesia also have reddish-gold hairs at the back of the head but it doesn't look like an Onesia. Any other angles will help.

Since you are from Poland, you could try to ask Krzysztof Szpila from Katedra Ekologii i Biogeografii. He may be able to recognize the species and better explain what you are seeing.