Order:
Wings and wing pads absent. Eye spots sometimes visible, but compound eyes absent. Segmented legs absent, but sometimes fleshy prolegs present. Sometimes with distinct head, often without head or with head drawn deeply into thorax. Body flattened, cylindrical, or maggot-like.
Family:
Mandibles move against each other along horizontal or oblique plane. Head complete and fully exposed. Hook-bearing prothoracic and anal prolegs paired, though division may be slight and only at apex. Spiracles absent (apneustic). Body segments usually without conspicuous dorsal tubercles and setae as in some Ceratopogonidae.