At first I thought I was chasing a hover-fly, until looking through the camera. The combination of the wing shape, the metallic body and the teeth on its back made it clear this was a new fly type I hadn’t seen before. It is a female Murky-legged black legionaire (Beris chalybata) , recognizable among others by the yellow legs. A new garden species!
Interesting as Soldier flies are in the prey range of Ectemnius caviforns, although this species has not been named particularly in literature references.
References1 Nederlands Soortenregister