Face without tubercles; in front of anterior ocellus without distinct depression; frons without pair of distinct depressions above antennal sockets, but whole frons may be depressed; occipital carina present laterally, not or slightly curved ventrally and remain removed from hypostomal carina (Figs 132, 142, 153, 163, 173, 183, 193), near level of middle of eye straight or nearly so, without transverse carina or crest; clypeus more or less convex and higher, usually narrower, or longer, not impressed; labrum normal, without emargination ventrally; scapus, fore coxa and trochanter at most weakly compressed; epistomal suture without large depressions; mandible asymmetrical and more or less abruptly widened basally (Figs 132, 142, 153, 163, 173, 183, 193), with rectangular or acute angle, rarely in males less developed (e.g. Opius ochrogaster); medio-posterior depression of mesoscutum variable; pronope round or wide elliptical, or pronotum only with a shallow transverse groove; scutellar sulcus usually rather wide; propodeum usually smooth or superficially sculptured; postpectal carina completely absent; vein 2-SR of fore wing present, rarely absent; first subdiscal cell of fore wing at least partly closed by vein 3-CU1 postero-apically (Figs 127, 137, 146, 158, 168, 178, 187); vein 1-M of fore wing usually straight; vein cu-a of hind wing nearly always present; vein 3-SR of fore wing distinctly longer than vein 2-SR; if subequal then vein m-cu of hind wing or precoxal sulcus (almost) absent; length of fore wing usually less than 3.5 mm; second and basal half of third tergite without sharp lateral crease, if sometimes weakly developed then second tergite smooth; length of second and third tergites combined less than 0.7 times length of metasoma behind first tergite; fourth and following tergites (at least partly) exposed; ovipositor sheath more or less setose basally.

Parasitoids of mining larvae of Agromyzidae, Anthomyiidae, Drosophilidae, Tephritidae, Ephydridae and Cecidomyiidae.

The asymmetrical (excluding ventro-basal carina) and more or less abruptly widened mandible is essential for the recognition of this group. Some opiine species may cause confusion because of a rather wide ventro-basal carina of the mandible but are excluded from Opius s.s. because the mandible itself (in ventro-lateral view) is gradually widened basally.