Diagnostic description.

Aulacus umbackae is a distinctive species that can be separated from other Australian species based on the combination of head shape in dorsal view, posterior margin convex, and mesosoma and metasoma orange.

Female. Body size 9.6 mm, ovipositor length 11.0 mm, fore wing length 9.1 mm (Fig. 81); colouration head black, mesosoma and metasoma orange, antenna black, flagellomeres 6–12 and mandibles cream-coloured, mesotarsus and hind leg dark brown, ovipositor sheaths black; wings hyaline, brownish tinge (Fig. 82G), hind wing veins spectral; head quadrate, width 1.4 × length, postocular space 0.5 × eye length in dorsal view (Fig. 82C), raised transverse carina above toruli absent, malar space 0.1 × height of eye (Fig. 82A); length of scape 1.5 × pedicel length, 1st flagellomere 1.5 × length of scape, 0.7 × 2nd flagellomere; mesosoma length 1.3 × height, mesoscutum in lateral view rounded antero-dorsally (Fig. 82D), length 0.8 × width in dorsal view (Fig. 82E); medial lobe rugose; ovipositor guide oblique, positioned medially (Fig. 82F); ovipositor sheath length 1.2 × fore wing length (Fig. 81); fore wing vein 2-Rs+M 0.8 × 1-Rs+M, four hamuli equidistant (Fig. 82G); metasoma pyriform,T1+T2 length 2.6 × width in dorsal view.