Gymnosoma clavatum mating · dygliamusės poruojasi
PL · zbójniczka łąkowa
https://en.wikipedia.org/wiki/Gymnosoma_clavatum
Gymnosoma species are difficult to distinguish so I am not sure for ID.
Adults can be found from May to October. These flies are endoparasites of various Pentatomidae species, on which the females lay their eggs. Larvae will develop inside bugs but usually do not kill the host.
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