Diagnostic description.

Aulacus dandenongensis can be distinguished from other Australian species based on the combination of body colouration black species, with cream-coloured base of hind tarsus, no ovipositor guide, mesoscutum length 0.8 (0.8) × width in dorsal view.

Female. Body size 8.9 (8.0–11.2) mm, ovipositor length 7.6 (6.0–7.9) mm, fore wing length 6.5 (6.5–8.5) mm (Fig. 21A); colouration black except fore and mid leg tarsomeres 1–4 cream-coloured, hind legs tarsomeres 1–2 cream-coloured, metasoma dark brown; wings hyaline except for an indistinct infuscation at apex 1st marginal and 4th submarginal cell (Fig. 22G), hind wing veins spectral; head shape quadrate, width 1.1 (1.4–1.5) × length, postocular space 0.5 (0.5) × eye length in dorsal view (Fig. 22C), raised transverse carina above toruli absent, malar space 0.2 (0.2–0.3) × height of eye (Fig. 22A); length of scape 1.7 (1.7) × length of pedicel, 1st flagellomere 1.5 (1.5) × length of scape, 0.6 (0.6) × 2nd flagellomere; mesosoma length 1.4 (1.3–1.4) × height, mesoscutum in lateral view rounded antero-dorsally (Fig. 22D); mesoscutum length 0.8 (0.8) × width in dorsal view (Fig. 22E); medial lobe strigate-rugulose; ovipositor guide absent (Fig. 22F); ovipositor sheath length 1.2 (0.9–1.2) × fore wing length (Fig. 21A); 2-Rs+M 0.6 (0.5–0.6) × 1-Rs+M, three hamuli, equidistant (Fig. 22G); metasoma clavate,T1+T2 length 5.4 (3.5–5.4) × width in dorsal view.

Males. Body size (10.0–11.3) mm, same as female (Fig. 21B).