Harmless flies and valuable pollinators, flower flies (in the family Syrphidae) are incredibly convincing mimics of bees, wasps, and yellowjackets. Coloration usually involves yellow, orange, or red plus black or brown, often with stripes or other patterns to mimic the warning coloration of bees or wasps. The bee mimics are fuzzy; the wasp and yellowjacket mimics are not. Syrphids (pronounced "surfids") are very common. They do not bite or sting. Recognize them as true flies by their single pair of wings, short antennae, and flylike compound eyes. This large group of true flies are famous for visiting flowers, hovering around them and intimidating people who think they might sting.
Larvae vary. Like the larvae of other flies, they are all technically maggots, but the different lifestyles involve different shapes. Larvae that live in polluted aquatic habitats have a remarkably long, tail-like anal breathing tube that reaches up to the water surface like a snorkel; these aquatic larvae are called "rat-tailed maggots." The syrphid larvae that eat aphids have a more typical maggot shape and are often greenish; and those that live in ant or wasp nests are flattened ovals.
Similar species: Although there are several other groups of true flies that mimic bees and wasps (including bee flies, robber flies, and many more), entomologists use details of wing venation and antenna structure to separate these families and genera with assurance. The rest of us compare photographs and illustrations in field guides to try identify these insects! If you are simply able to distinguish a syrphid fly from a bee or a wasp, pat yourself on the back.