Opomyzidae is a family of acalyptrate Diptera. They are generally small, slender, yellow, brown or black coloured flies. The larval food plants are grasses, including cereal crops, the adults are mainly found in open habitats. Some species being agricultural pests.
For terms see Morphology of Diptera. Small slender yellow, brown, reddish or black flies. The narrow wings are usually with light or dark-colored spots (darkly marked crossveins apical spot). Head with one pair of backwardly directed orbital (frontal bristles) bristles. Scattered interfrontal setulae are present Ocellar bristles are present. Postvertical bristles are absent (rarely present). Vibrissae absent but Geomyza with a strong bristle near the vibrissal angle. Ocelli are present and the arista is pubescent or with long hairs. Tibae without preapical dorsal bristles. R1 is short, the subcosta ends near the break of the costa (usually incomplete but apical part sometimes visible as a faint line reaching the costa) and near apex of R1;posterior basal wing cell and anal cell are small. The crossvein BM-Cu is present but usually incomplete. Tibiae without dorsal preapical bristle.
The larvae live in the stems of grasses, a few species being a pest in agriculture, for instance Opomyza florum, the Yellow Cereal fly. Damage caused by Opomyzidae to Gramineae is termed "dead heart".