I’ve talked quite a bit about bee–mimicking flies, but flies are also known to mimic wasps. Here’s an example of a fly that I think does a particularly good job of it…mimicking the constricted waist that is supposedly one of the diagnostic characters of Hymenoptera (wasp-waist).
I think it does quite a good job of looking like a wasp! The species is Physocephala tibialis. It is supposedly a parasite on the bumblebee, Bombus bimaculatus.
But note the halteres, which are fairly obvious in this photo.
It is visiting Mountain Mint, or Pynanthemum tenuifolium.