We've been seeing a lot of bee flies in the genus Geron in our yard lately (link is to previous post).
Geron bee flies are more slender than most of their relatives and have a "humpbacked" appearance because their thorax bulges up in the back (dorsal surface).
As stated at BugGuide, the adults use their long, prominent proboscis to drink nectar from flowers. They seem to prefer sunflowers.
Because of their fuzzy bodies, they pick up pollen while feeding on nectar. When they carry the pollen to another flower, they help pollinate it.
Looking closely, I noticed some caterpillars. Bee flies are parasites of other insects in general. Geron bee flies are parasites of caterpillars. These adults were probably looking for a caterpillar to lay their eggs on.
I'm going to spend some time watching the caterpillars to see if I can find out more. Look for an upcoming post about them.
Until then, do you have Geron bee flies in your yard? What flowers are they visiting?