When I first began taking photos of insects, I figured that every black and yellow insect flying around flowers was a bee. I was naive, of course, and over time I came to realize that there was another whole family of insects called hover flies (or flower flies or syrphids) that are bee mimics and nectar on flowers. Although their name may suggest that they feed while hovering, like hummingbirds, the hovering seems to be primarily a means for finding a food source.
Last week I spotted some hover flies during a visit to Occoquan Bay National Wildlife Refuge that were feeding on the wild flowers in bloom. I think that they may be American Hover Flies (Eupeodes americanus), but I confess that I am not really familiar with the different species of hover flies. According to Wikipedia about 6000 species of hover flies have been described in 200 genera and hover flies can be found on every continent in the world except for Antarctica.
I did not have a macro lens on my camera, so I was pleasantly surprised to capture such a detailed shot of the tiny hover fly. If you click on the image, you will get a closer view of some of those details of the hoverfly that was intently at work, as “busy as a bee.”
© Michael Q. Powell. All rights reserved.
Mike Powell 
I remember being in a wet meadow full of beggar’s ticks plants in full bloom and becoming apprehensive at the buzzing sounds of flying insects on the flowers. I thought I had stumbled into a swarm of bees. But it turned out they were hover flies. All kinds of them.
A book I have found useful in identifying syrphids is the Field Guide to the Flower Flies of North America. It has tons of photos of the flies showing body patterns, wing venation, and other features for identifying them.
Thanks, Gary, for the tips about the guide to flower flies, and for the info about your fascinating encounter with a whole host of hover flies of various kinds.