Here is more than many people want to see: details of behavior and structure of a beefly, gathering pollen from the flower of a weedy hawksbeard (Crepis vesicaria ssp. taraxacifolia).
I was focused on this flower when a beefly landed. So, I carried on. The beefly didn't seem to mind the big camera lens moving about in the neighborhood. I captured many images; here is a selection.
Note the tongue -- its shape (forked at the end, or with a semicircle?) and action as it collects pollen. Many details of the beefly structure, including the halteres, and the three simple eyes between the large compound eyes. Perhaps these simple eyes help the fly avoid predators -- hard-wired to the brain for quick response, no time spent on decoding the complex signals from the compound eyes. Just my guess.
The halteres help in flying and maneuvering. Like gyroscopes.