1	Inner side of metafemur with a row of spinae (Suppl. material 1: Fig. S5A). Male with two fossette (small apical one on the inner side, and a large one on the outer side) (Suppl. material 1: Fig. S10A, B); mesocoxa with 1–3 long pile posteriorly	Merodon eumerusi Vujić, Radenković & Likov, 2019
–	Inner side of metafemur without a row of spinae	2
2	Terga partly brown, reddish or yellow	22
–	Terga black	3
3	Females (genitalia not visible)	13
–	Males (genitalia visible externally)	4
4	Male genitalia without ctenidium at hypandrium (Suppl. material 2: Fig. S7K: marked with arrow); small sized species (5–9 mm) with metallic shiny body and distinctly dichoptic eyes, separated by distance almost as long as distance between ocelli (Suppl. material 1: Fig. S11A); metafemur with very small apical triangular lamina apicoventrally (Suppl. material 1: Fig. S12A: marked with arrow)	fulcratus species group
–	Male genitalia always with ctenidium at hypandrium (as in Suppl. material 2: Fig. S7C: marked with arrow)	5
5	Large species (15–20 mm) with long body pilosity and broad metafemur covered with long pile (Suppl. material 1: Fig. S12B); basoflagellomere elongated; terga usually covered with pile in different combinations of colours (white, yellow or black) (Suppl. material 3: Fig. S9A, B); surstyle with well-defined and large anterior and posterior lobes (Suppl. material 2: Fig. S7A: al, pl)	clavipes species group
–	Species with shorter pilosity and different combinations of characters	6
6	Sternum 4 medially clearly divided with membranous structure and with posterolateral tubercles or laminate extensions (Suppl. material 1: Fig. S11C: marked with arrow); sternum 4 from lateral view usually fin-form (Suppl. material 1: Fig. S11D: marked with arrow); basotarsomere of metatarsus usually expanded (Suppl. material 1: Fig. S12C, D) and/or with strong setae ventrally (Suppl. material 1: Fig. S12C, D: marked with arrow)	tarsatus species group
–	Sternum 4 and basotarsomere of metatarsus without such modifications	7
7	Male genitalia: posterior surstyle lobe divided into two branches (Suppl. material 2: Fig. S9J: pl); eyes slightly dichoptic, distance between eyes about two facets long (Suppl. material 1: Fig. S11B)	Merodon hirtus Sack, 1932
–	Male genitalia: posterior surstyle lobe not divided into branches; eyes holoptic	8
8	Abdomen elongated and narrow; terga black; terga 2–4 with a pair of pollinose fasciate maculae (Suppl. material 1: Fig. S11E); metafemur usually long and narrow. Male genitalia: hypandrium with very long lingula (Suppl. material 2: Fig. S6C: l); posterior surstyle lobe with inner lobe covered with long and strong setae (Suppl. material 2: Fig. S6B)	aberrans species group
–	Species with different combinations of characters	9
9	Basoflagellomere elongated, at least three times as long as wide (Suppl. material 1: Fig. S13A); posterior surstyle lobe quadratic (Suppl. material 2: Fig. S7D: pl)	italicus species group (in part)
–	Basoflagellomere less elongated; posterior surstyle lobe different	10
10	Posterior surstyle lobe with basolateral protrusion (lateral hump) (Suppl. material 2: Fig. S9G: marked with arrow). Metafemur with shorter pilosity ventrally, shorter than width of metafemur (Suppl. material 1: Fig. S14A); basoflagellomere narrow and elongated, two times longer as pedicel (Suppl. material 1: Fig. S13B)	serrulatus species group (in part) (Vujić et al. 2020b)
–	Posterior surstyle lobe of male genitalia without basolateral protrusion (lateral hump)	11
11	Basoflagellomere reddish-yellow (Suppl. material 1: Fig. S13C); tarsus of metaleg yellow (at least basotarsomere) (Suppl. material 1: Fig. S14B); metatarsus long, more than three times longer than wide (Suppl. material 1: Fig. S14B); metafemur less incrassate, ca. four times longer than wide (Suppl. material 1: Fig. S14B)	Merodon ottomanus Hurkmans, 1993
–	Basoflagellomere brown to black; tarsi of metaleg dark; metatarsus shorter, two times longer than wide (Suppl. material 1: Fig. S14D); metafemur more incrassate, ca. three times longer than wide (Suppl. material 1: Fig. S14C)	12
12	Basoflagellomere with convex dorsal margin (Suppl. material 1: Fig. S13D); posterior surstyle lobe with the apical hump directed towards cercus (Suppl. material 2: Fig. S10G: marked with arrow)	Merodon clunipes Sack, 1913 (in part)
–	Basoflagellomere with concave dorsal margin (Suppl. material 1: Fig. S13E); posterior surstyle lobe without the apical hump directed towards cercus (Suppl. material 2: Fig. S10A: pl)	Merodon auronitens Hurkmans, 1993
13	Metafemur more incrassate, ca. three times longer than wide, covered with dense pilosity (Suppl. material 1: Fig. S15A)	14
–	Metafemur less incrassate, at least three times longer than wide (as in Suppl. material 1: Fig. S15B)	15
14	Basoflagellomere shorter, 1.3 times as long as wide, with convex dorsal margin (Suppl. material 1: Fig. S16A); pile on ventral margin of metafemur shorter, ca. one third of width of metafemur (Suppl. material 1: Fig. S15A)	Merodon clunipes Sack, 1913 (in part)
–	Basoflagellomere elongated, two times as long as wide (Suppl. material 1: Fig. S16B); pile on ventral margin of metafemur longer, ca. half of width of metafemur (Suppl. material 1: Fig. S15C)	clavipes species group (in part)
15	Small sized species (8-11 mm) with metallic shiny body; scutum and terga strongly punctate, without or with very weak pollinose areas (Suppl. material 1: Fig. S17A, B); metafemur with very small apical triangular lamina apicoventrally (Suppl. material 1: Fig. S15D marked with arrow)	fulcratus group
–	Species with different combinations of characters	16
16	Metafemur with short pilosity (Suppl. material 1: Fig. S15E)	serrulatus species group (in part) (Vujić et al. 2020b)
–	Metafemur with longer pile (as in Suppl. material 1: Fig. S15B)	17
17	Abdomen broad, oval (Suppl. material 1: Fig. S17C); terga without pollinosity or with very weak pollinose fasciate maculae; tarsus of metaleg yellow (at least basotarsomere) (Suppl. material 1: Fig. S15B)	Merodon ottomanus Hurkmans, 1993
–	Species with different combinations of characters	18
18	Basotarsomere of metatarsus elongated, four times as long as wide (Suppl. material 1: Fig. S15F); basoflagellomere elongated, 2.5 times as long as wide (Suppl. material 1: Fig. S16C); tarsi yellow, tibiae mostly yellowish, except medially brown (Suppl. material 1: Fig. S15F)	Merodon murinus Sack, 1913 (in part)
–	Species with different combinations of characters	19
19	Abdomen narrow, elongated (Suppl. material 1: Fig. S17D); metaleg usually narrow (as in Suppl. material 1: Fig. S18A)	aberrans species group
–	Species with broader abdomen and metaleg	20
20	Tergum 2 without or with indistinct narrow pollinose fasciate maculae (Suppl. material 1: Fig. S19A, B); basotarsomere of metatarsus usually expanded (Suppl. material 1: Fig. S18B) or with strong setae ventrally (Suppl. material 1: Fig. S18B marked with arrow)	tarsatus species group
–	Tergum 2 with broad pollinose fasciate maculae (Suppl. material 1: Fig. S19C); basotarsomere of metatarsus not expanded and without strong setae ventrally (Suppl. material 1: Fig. S18C)	21
21	Terga 2–4 strongly punctate; second and third tarsomeres similar in size (Suppl. material 1: Fig. S18D marked with arrow); sterna shiny	Merodon auronitens Hurkmans, 1993
–	Terga 2–4 finely punctate; second tarsomere longer than third (Suppl. material 1: Fig. S18C marked with arrow); sterna dull	Merodon hirtus Sack, 1932
22	Females (genitalia not visible)	31
–	Males (genitalia visible externally)	23
23	Metatibia swollen in apical half (Suppl. material 1: Fig. S20A); basotarsomere of metatarsus strongly modified (Suppl. material 1: Fig. S20A)	Merodon caudatus Sack, 1913
–	Metaleg without such modifications	24
24	Posterior surstyle lobe with basolateral protrusion (lateral hump) (Suppl. material 2: Fig. S9G: marked with arrow)	serrulatus species group (in part) (Vujić et al. 2020b)
–	Posterior surstyle lobe without basolateral protrusion	25
25	Face with a bulge below antennae (Suppl. material 1: Fig. S21A: marked with arrow); posterior surstyle lobe hook-like (Suppl. material 2: Fig. S10J: pl)	Merodon crassifemoris Paramonov, 1925
–	Face without a bulge below antennae	26
26	Metatrochanter without calcar	28
–	Metatrochanter with distinct calcar (Suppl. material 1: Fig. S20B: marked with arrow)	27
27	Basoflagellomere 1.2 times as long as wide (Suppl. material 1: Fig. S23A); body pilosity very short; terga 3–4 dark (Suppl. material 1: Fig. S22A)	aurifer species group
–	Basoflagellomere short, as long as wide (Suppl. material 1: Fig. S23B); body pilosity longer; terga 3–4 mostly yellow-red (Suppl. material 1: Fig. S22B)	pruni species group
28	Basoflagellomere elongated, at least three times as long as wide (Suppl. material 1: Fig. S13A); posterior surstyle lobe quadratic (Suppl. material 2: Fig. S7D: pl)	italicus species group (in part)
–	Basoflagellomere shorter, less than three times as long as wide (as in Suppl. material 1: Fig. S23C); posterior surstyle lobe different	29
29	Eye contiguity very short, approximately four to five facets long (Suppl. material 1: Fig. S21B); male genitalia in Suppl. material 2: Fig. S11D–F	Merodon murinus Sack, 1913 (in part)
–	Eye contiguity more than 10 facets long (as in Suppl. material 1: Fig. S21C); male genitalia different	30
30	Tarsi yellow dorsally and ventrally (Suppl. material 1: Fig. S20C, D)	avidus species group (Popović et al. 2015; Ačanski et al. 2016b; Likov et al. 2020)
–	Tarsi dark brown/black dorsally and orange/brown ventrally (Suppl. material 1: Fig. S20E, F)	nigritarsis species group (Vujić et al. 2013; Likov et al. 2020)
31	At least terga 2 and 3 with brown, reddish or yellow markings	36
–	Only tergum 2 with brown, reddish or yellow maculae, other terga dark	32
32	Metatibia swollen in apical half (Suppl. material 1: Fig. S24A); tarsomeres of mesotarsus with strong, black lateral setae (Suppl. material 1: Fig. S24B)	Merodon caudatus Sack, 1913
–	Metatibia of normal shape (as in Suppl. material 1: Fig. S24C); tarsomeres of mesotarsus without such lateral setae	33
33	Pile on ventral margin of metafemur dense and long, the longest as long as width of metafemur (Suppl. material 1: Fig. S15C)	clavipes species group
–	Pile on ventral margin of metafemur shorter, maximum as long as half of width of metafemur (as in Suppl. material 1: Fig. S15A)	34
34	Basoflagellomere shorter, 1.3 times as long as wide, with convex dorsal margin (Suppl. material 1: Fig. S16A); metafemur incrassate or swollen, ca. three times longer than wide (Suppl. material 1: Fig. S15A)	Merodon clunipes Sack, 1913 (in part)
–	Basoflagellomere longer, with straight or concave dorsal margin (Suppl. material 1: Fig. S16C); metafemur less incrassate	35
35	Tarsi yellow, tibiae mostly yellowish, only medially brown; frons and vertex usually partly reddish to yellow (Suppl. material 1: Fig. S25A)	Merodon murinus Sack, 1913 (in part)
–	Legs mostly black, at least tarsi dark; frons black	serrulatus species group (in part) (Vujić et al. 2020b)
36	Basoflagellomere elongated, more than 1.5 times as long as wide (Suppl. material 1: Fig. S26B); metatrochanter with rounded ventral margin (as in Suppl. material 1: Fig. S24D)	38
–	Basoflagellomere shorter, less than 1.3 times as long as wide (Suppl. material 1: Fig. S26A); metatrochanter with angular ventral margin (Suppl. material 1: Fig. S24C: marked with arrow)	37
37	Basoflagellomere very short, as long as wide (Suppl. material 1: Fig. S26A); metafemur dorsally and ventrally covered with longer outstanding pile (Suppl. material 1: Fig. S24C)	pruni species group
–	Basoflagellomere longer, 1.2 times as long as wide (Suppl. material 1: Fig. S26C); metafemur covered with short and adpressed pilosity (Suppl. material 1: Fig. S24E)	aurifer species group
38	Face with a bulge below antennae (Suppl. material 1: Fig. S25B: marked with arrow)	Merodon crassifemoris Paramonov, 1925
–	Face without a bulge below antennae	39
39	Basoflagellomere elongated, at least 2.7 times as long as wide (Suppl. material 1: Fig. S26D); terga 2 and 3 reddish (Suppl. material 1: Fig. S25C)	italicus species group (in part)
–	Basoflagellomere shorter, less than 2.5 times as long as wide (as in Suppl. material 1: Fig. S26E)	40
40	Tarsi yellow dorsally and ventrally (as in Suppl. material 1: Fig. S20C, D)	avidus species group (Popović et al. 2015; Ačanski et al. 2016b; Likov et al. 2020)
–	Tarsi dark brown/black dorsally and orange/brown ventrally (as in Suppl. material 1: Fig. S20E, F)	nigritarsis species group (Vujić et al. 2013; Likov et al. 2020)