Adult flies of many species in this family are mimics of bees or wasps. They are mostly black with yellow or orange stripes. A few others are brown, or metallic green or blue (these may also be mimics of bees). They have large eyes and short mouthparts formed into a tube with a sponge at the end. Their bodies may be slim or stout and are sometimes flattened top-to-bottom. Some species wag they abdomens up and down when they land. Like all flies they only have two wings, their hind wings are reduced (see More Information about True Flies for more).

Larvae are more variable. They are all legless and headless, but some aquatic species have long breathing tubes on their hind ends, some have tough skins, some look like little slugs. Color varies from white to brown to green.

Range length: 4.0 to 25.0 mm.

Other Physical Features: ectothermic ; bilateral symmetry

Sexual Dimorphism: sexes alike; female larger