First record from the western Palaearctic.

Morphological abbreviations: ad: anterodorsal; av: anteroventral; pd: posterodorsal; pv: posteroventral; vt: ventral; fore leg: leg I; mid leg: leg II; hind leg: leg III; 5 tarsal segments with tarsomere (I–III)₁ as most basal and tarsomere (I–III)₅ as most apical.

Diagnosis: at first sight similar to Hercostomus parvilamellatus (Macquart, 1827), but face with two strong bristles (absent in H. parvilamellatus), veins R₄₊₅ and M₁ parallel (distinctly converging in H. parvilamellatus), and clutch of minute setae in front of posterior spiracle (absent in H. parvilamellatus).

Description: Head. Face silvery grey, parallel-sided, rather wide, 1.3x as wide as postpedicel length, with diverging shallow ridges on basis; bare, with 2 strong (1.2x as long as postpedicel length), curved black bristles on rim between epistoma and clypeus (Fig. 2B), and with 3 minute, yellow setae on lower 1/2 of epistoma. Frons dusted grey, with brownish tinge. Occiput brownish black, slightly dusted grey, convex. Palp small, about 1/7 of eye height, ovoid, brownish black, with pale pubescence and 1 strong, black apical bristle. All postocular bristles black. Two pairs of small, black postocellar bristles. Antenna black, with scape pubescent dorsally, and pedicel with ring of bristles at apex. Postpedicel rounded ovoid, with blunt apex; slightly longer than scape and pedicel combined. Arista rather robust and distinctly pubescent, inserted dorsally at apical 1/3, 1.5x as long as first three antennal segments combined.

Thorax and abdomen. Mesonotum, including scutellum, and abdomen brownish black, with dark green reflection; all bristles black unless otherwise mentioned. Pleura dusted greyish, with a clutch of 3 minute, erect setae in front of posterior spiracle. Eight strong acrostichal bristles, biserial, reaching 5^th dorsocentral bristles posteriorly, latter distinctly medially off-set. Six dorsocentral bristles; further complete dolichopodine chaetotaxy of mesonotum. Scutellum with 2 strong black median bristles, 2 minute, pale lateral setae and a sparse black pubescence both on disk and margin. Upper propleura with about 6 minute, yellow setae; lower propleura with one strong, black, prothoracic bristle. Five abdominal tergites visible and pubescent.

Wings slightly smoky, with veins R₄₊₅ and M₁ parallel towards wing apex; proximal section of M₁ 0.7x as long as apical section; proximal section of CuA₁ 1.5x as long as apical section; apical section of CuA₁ 2.3x as long as outer crossvein dm-cu. Halter yellowish white. Squamal fringe black.

Legs. All bristles and setae black. Coxae and trochanters brownish black; coxa II with narrow yellowish white apical edge. All femora brownish black, yellowish only at extreme apex. Coxa III with strong erect bristle at centre, and with 3 minute dark se-tae. Femur I with multiple rows of small inclined vt bristles on basal 1/4, about as long as 1/3 of femur depth; with three small preapical pv bristles. Femur II with one strong black ad preapical bristle; with multiple rows of small inclined vt bristles on basal 1/3, about as long as 1/3 of femur depth. Femur III with one strong black ad preapical bristle and one small black av preapical bristle; with multiple rows of small inclined bristles on basal 1/2, less than 1/3 as long as femur depth. Tibia I yellow, brownish on basal 1/4; with 1 ad bristle at about basal 1/3, followed by a serration of black bristles to apex; with 2 pd bristles at about basal 1/4 and 1/2. Tibia II yellow with basal 1/4 brownish; with 3 ad bristles at about basal 1/4, 2/5 and 2/3, 2 pd bristles at basal 1/4 and 2/3, and one av bristle at basal 3/5; all bristles 1.7–2.0x as long as tibial depth, except for smaller basalmost ad bristle; with 4 large and one small apical bristles. Tibia III yellowish brown, with basal 1/6 and apical 1/3 brown; with 3 ad bristles at basal 1/4, 1/2 and 2/3, and 3 pd bristles at basal 1/5, 2/5 and 3/5; all bristles about 2x as long as tibial depth; with one strong dorsal preapical bristle and a dense pd pubescence on apical 1/2; with 2 strong and one small apical bristles; with one vt bristle at about basal 2/3, 1.4x as long as tibial depth. Tarsus I dark brown with taI₁ pale yellow on basal 1/2. Tarsus II dark brown with taII₁ pale yellow on basal 2/3. Tarsus III dark brown with taIII₁ pale yellow on less than basal ½. Length ratio of femur/tibia/ ta₁/ta₂/ta₃/ta₄/ta₅ of leg I: 7.7/7.8/3.5/1.5/1.3/1/1, of leg II: 7.5/8.3/3.5/1.9/1.4/1/1, and of leg III: 7.5/9.4/1.8/3.6/1.9/1.3/1.

Body length: 2.0 mm, wing length: 2.5 mm.

Remarks: the only non-gender related features of S. setifacies that differ from those of the female specimen described above are: an entirely brown femur and tarsus III, an entirely yellow tibia I and II, and 4 pd bristles on tibia III. As all of these characters are known to show intraspecific variation in Dolichopodidae, it remains probable (but not sure) that the Poľana female might indeed belong to S. setifacies.

The clutch of minute setae in front of the posterior spiracle (character no. 15 in Brooks 2005) is rather inconspicuous as a diagnostic character, but represents the key character (synapomorphy) for the monophyly of the Dolichopus genus group sensu Brooks (2005), encompassing Dolichopus, Ethiromyia and Gymnopternus. Despite the fact that this clutch has been encountered in some species of Tachytrechus and Apelastoneurus as well, it is very likely that Setihercostomus also belongs to the above genus group when considering other characters like e.g. the parallel course of the R₄₊₅ and M₁ veins (also present in Ethiromyia and Gymnopternus). This clutch of minute seate has not been mentioned in the description of any of the four Setihercostomus species, but it is assumed that it has simply been overlooked by the respective authors.