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Northern Germany, Schleswig-Holstein, Schenefeld near Hamburg, walking path along the rivulet Düpenau, on a wooden case, called "Hotel for Insects" where especially bees fly in and out. Length of the fly 5mm; 9th of May 2021, Photos: kuv.
I watched a fly first waiting before a bee hole, then going backwards in the hole. I think it is a parasit of bees. Please help to get the ID.
Greetings Kuv