Key to species of the genus Hercostomus from Japan (males)

1 Acrostichal setae absent. Fore and mid tarsi with erect ventral hairs. R4+5 sharply curved in apical part. Tarsomeres 4 and 5 of fore tarsus widened (Fig. 8 I)....................................... Hercostomus zhenzhuristi Smirnov & Negrobov

- Acrostichal setae present, arranged in two rows. Fore and mid tarsi without erect ventral hairs. R4+5 slightly curved or almost straight............................................................................................. 2

2 Postocular setae yellow................................................................................ 3

- Postocular setae black................................................................................. 5

3 Thorax and abdomen with silvery pollinosity. Tarsomeres 4 and 5 of mid leg widened (Fig. 8 E)................................................................................................ Hercostomus spathulatus sp. nov.

- Thorax and abdomen without silvery pollinosity. Tarsomeres of mid leg not widened.............................. 4

4 Antennae black. Coxae black............................................................ Hercostomus lii Wei

- Antennae mostly yellow (Fig. 8 G). Coxae yellow........................ Hercostomus flaveolus Negrobov & Chalaya

5 Thorax and abdomen partly yellow....................................................................... 6

- Thorax and abdomen mostly green....................................................................... 8

6 Hypopygium dark (Fig. 8 D)................................................. Hercostomus nigricollaris sp. nov.

- Hypopygium yellow.................................................................................. 7

7 Only abdominal segments 1–3 partially yellow......................... Hercostomus flaviventris Smirnov & Negrobov

- All segments of abdomen yellow laterally (Fig. 8 B)................................... Hercostomus falcilis sp. nov.

8 Tarsomere 1 of hind leg with black curved spine (Figs 1 F, 8A)....................... Hercostomus acutiformis sp. nov.

- Tarsomere 1 of hind leg without curved spine.............................................................. 9

9 Antennae mostly yellow (Fig. 8 E)............................................ Hercostomus spinitibialis sp. nov.

- Postpedicel black..................................................................................... 10

10 Antennae black. Hind femur without black spot at apex.................... Hercostomus takagii Smirnov & Negrobov

- Scape yellow below. Hind femur with black spot at apex (Fig. 8 C)................... Hercostomus flavipalpus sp. nov.