I call them twilight bees because they only seem to show up in the yard at dusk, when the datura (angel trumpets) open. On a typical evening, several dozen flowers open, which means hundreds of bees. They are very docile, stay around for only fifteen minutes or so before it gets too dark, and let me garden around them. I'm able to snip dead flowers and prune back a plant that has a dozen or more bees circling around it, without any of us being bothered.
The camera didn't want to stay in focus, as the gals kept flying straight at me. The noise drowning out their buzzing is from the cicadas, which begin their song about three o'clock.