It appears as if there were two individuals on one adult female meloe proscarabeus. I can't seem to find any notes on hyperparasitic dipterans feeding on meloe species. Unfortunately I just stumbled upon those hitchhikers while reviewing the footage, I didn't take note of them while photographing. Hence the quality. The beetle was alive, but not in the best condition (missing antenna).
Under a rock ledge next to a flowing stream.