Adults: Small, delicate, elongate flies; length typically about 2 mm. Wings deciduous, narrow, fringed with long macrotrichia; venation reduced. Legs similar, long and thin; femur and tibia superficially bi-segmented. Terminalia directed ventrad. Larva: Body typically 1 to 2 mm in length, compressed laterally, lightly sclerotized except head capsule, which is well developed and visible (eucephalic). Antenna elongate, one-segmented. Thoracic segments distinct; appendages absent. Abdomen nine-segmented; segments I-VII and IX with paired, crochet-tipped ventral prolegs. Anal papillae four in number. No specialized breathing apparatus (apneustic). Body surface mostly glabrous, with few setiform sensilla.