Key to species of the M. filiformis species-group

1- First metasomal segment exceptionally long, longer than mesosoma, and almost linear in dorsal view (Fig. 4); pronotal carina in dorsal view smoothly curved medially, projecting at sides as relatively low and round humeral lobes (Fig. 22); sculpture of mesosoma stronger (Fig. 22)....................................................... M. filiformis (de Saussure)

1’- First metasomal segment shorter than mesosoma; pronotal carina often with a straight sector medially (Figs 23–27), humeral lobes a little larger and more salient, rather quadrate......................................................... 2

2- First metasomal segment roughly linear in dorsal view, about as long as [mesoscutum + scutellum + metanotum] (Figs 13, 31); claws of hind tarsus symmetrical (Fig. 33a)................................................................ 3

2’- First metasomal segment shorter than [mesoscutum + scutellum + metanotum]; claws of hind tarsus asymmetrical (Fig. 33b) ................................................................................................... 4

3- Ground color black with a few yellow marks (Figs 27, 29, 31).................................... M. nazgul sp. nov.

3’- Ground color yellow with black to brown marks (Figs 13, 19, 25)................................. M. asahi sp. nov.

4- Size large, fore wing length ca. 12mm; first metasomal segment linear basally, with sides diverging only after spiracles (Fig. 8); propodeal furrow narrow, propodeal valve high and narrow, with round margin; color yellow with black to brown marks (Fig. 8, 15, 17)........................................................................... M. omicron Richards

4- Size small; first metasomal segment with sides diverging from a point anterior to spiracles; propodeal furrow wider, propodeal valve wider below, more triangular in shape................................................................ 5

5- Ground color black with few yellow marks (Figs 9, 20, 23, 28)................................. M. buyssoni (Ducke)

5’- Color yellow with black to brown marks.................................................................. 6

6- Gena wide; humeral lobes less prominent; hind tibia and tarsus black; disks of metasomal terga light testaceous above (Figs 10, 11).............................................................................. M. napoensis Richards

6’- Gena very narrow, poorly visible in lateral view; humeral lobes more prominent; hind tibia light brown with yellow marks; hind tarsus light brown to black apically; metasomal terga 1–6 dark brown to black above (Figs 12).. M. kallindusfloren sp. nov.