Vockeroth (1969) provided an excellent diagnosis of this genus.
Medium to large, moderately slender to robust species with very clear wings, oblique and often lunulate abdominal maculae, and usually with strongly swollen frons in male. Eye densely haired although as much as posterior half sometimes almost bare in female. Dorsal 2/3 of eye of male with an extensive area of almost uniformly enlarged facets, this area anteriorly reaching the margin of the eye above and progressively farther from it below, posteriorly narrowly separated from margin throughout; facets much less enlarged in occidentalis Shannon than in other species. In all species but occidentalis front of male greatly broadened, strongly swollen, and with abundant erect black hairs, eyes meeting anteriorly at an angle of 135°-145°. In occidentalis front of male only slightly broadened and swollen but with moderately conspicuous black hair, eyes meeting anteriorly at an angle of 120°. Front of female only slightly swollen but very broad, at vertex from 0.28 to 0.32 head width. Face in both sexes moderately to strongly swollen, sometimes more strongly produced below, with moderately large and sometimes slightly compressed tubercle; face at its widest point from 0.50 to 0.66 times as broad as head. Face bright to pale yellow, usually with narrow brown to black median vitta which always ends just above the tubercle. Basoflagelloemere from 1.4 to 1.9 times as long as broad. Scutum shining black, always pale pilose, usually very obscurely yellowish laterally, rarely with well-defined, entire, pale yellow, lateral margin. Scutellum with the disc or rarely the entire surface translucent, dull yellow to dark yellow-brown usually with a narrow to broad posterior margin opaque and slightly paler. Pleura black, densely pale pilose, subshining to moderately pollinose, sometimes with posterodorsal corner of anepisternum distinctly yellowish. Dorsal and ventral katepisternal pile patches narrowly to broadly joined posteriorly and rarely narrowly joined anteriorly, otherwise narrowly separated; the ventral patch extending much farther dorsad than usual, anteriorly extending broadly anterodorsad to dorsoanterior corner of katepisternum. Metasternum bare. Vein R4+5 usually very broadly and shallowly dipped into cell R4+5 more rarely nearly straight. Microtrichia greatly reduced, absent from at least basal half of wing and usually from almost entire wing; usually at least a few short, weak, erect, scattered microtrichia present near posterior wing margin, rarely such microtrichia sparsely present on outer half of wing. Abdomen narrowly to broadly oval, flattened, strongly margined from just beyond base of tergite 2 to apex of tergite 5. Tergites 2 to 5 each with a pair of slightly to strongly oblique, narrow to broad, whitish-yellow to bright yellow maculae which usually are clearly separated from the lateral margin; maculae of tergites 3 to 4 at least slightly, and usually strongly, lunulate. Sternites very variable in colour; usually yellow, with or without transverse black median bands or longitudinal lateral and median stripes, rarely black with broad yellowish-white incisures. In melanostoma (Macq.) only, the yellow maculae of the tergites, and the entire surface of the sternites, when viewed obliquely from in front, show transverse striae of very fine pale pollen (Vockeroth 1969).
Adapted from Dusek and Laska (1985).
MALE.
Head: Eye densely hairy, hairs about 0.25 mm long. Anterior angle of approximation of eyes wide, 120º-136º. Frons inflated. Face broad occupying 51-56% of head width. Face not produced. Some black hairs usually present around facial tubercle.
Thorax: Scutum black with lateral margins, at most vaguely brownish or yellowish. Anepisternum and Katepisternum black, slightly dusted. Apical margin of wing membrane with microtrichia very scarce. Vein R4+5 strongly dipped, point of meeting of vein R2+3 and margin of wing and point of meeting of vein R4+5 and dorsal marginal cross-vein about equally distant from base of wing. Profemur with pale hairs only. Mid of metatibia usually with dark macula.
Abdomen: Yellow macula on terga 3 and 4 with anterior margin deeply concave and posterior margin strongly convex, usually with apparent posterolateral corner. Inner and outer end of maculae about equidistant from base of tergum. Male genitalia: Epandrium similar as in S. pyrastri distinguishing by rather more slender and longer paralobi. Hypandrium in front view broadest above, below regularly rounded, higher than broad (high about 0.6 mm, width above 0.5 mm and in lower third 0.4 mm). Lingula of hypandrium very long, sharp. Pointed elevations of posterior side of hypandrium unregular and rather distinctly elevated. Surstyli bearing one tooth, less frequently two teeth. Teeth of base of aedeagus not very distant about the same size. Aedeagus with funnel-like broadened tubus and with very fine thorns on lower side.
FEMALE.
Eye with hairs somewhat shorter, about 0.15 mm. Face occupying about 48 -50% of head width, vertex about 22-25% of head width. Variation of colour influenced by temperature. As in other species of Syrphinae up to now bred (Dusek and Laska 1974) the specimens bred from puparia kept in higher temperature are paler. In specimens bred at 10 ºC the yellow maculae on terga 2, 3 and 4 are separated from the side margin of tergum and the maculae are comparatively narrow. In specimensbred at 25 ºC these maculae are larger and reach the side margin of tergum.
Laska et al. (2006) were the last authors to study in deep the taxonomy of this genus. They concluded to divide Scaeva into two subgenera, Semiscaeva and Scaeva, based on morphological characters of the immature stages. One group (S. dignota, S. selenitica, S. mecogramma) has a distinct angle of about 90° between orificia II and III, as is typical for other related genera of Syrphini. A second group (S. pyrastri, S. albomaculata, S. latimaculata) has the orificia II and III (on spiracular plate) parallel, with insertion of orificium III beneath the level of insertion of orificium II (probably apomorphic situation).
Due to the impossibility to assign any different species with unknown larva to either group, I do not find the subgenera helpful for the taxonomy of the genus Scaeva, and at this moment both groups can be referred as species groups.
Synonyms:
Syrphus seleniticus Meigen, 1822: 304.
Scaeva selenitica (Meigen, 1822).
Meigen, J.W. (1822) Systematische Beschreibung der bekannten europaischen zweiflugeligen Insekten. Dritter Theil. Schulz-Wundermann, Hamm. x + 416 pp., pls. 22-32.
GenBank accession number for this species are: protein-coding COI gene (AY603764), rRNA 28S gene (EF127404) and internal transcribed spacer 2a (partial sequence) + 2S ribosomal RNA gene (complete sequence) + internal transcribed spacer 2 (partial sequence) (DQ158896; DQ158895).
Body length: 11-16 mm (Dusek and Laska 1985).
Dusek and Laska (1967) placed Scaeva, in their scheme, as sister group of Scaevosyrphus [=Eupeodes (Metasyrphus)], Lapposyrphus, Posthosyrphus [=Eupeodes (Metasyrphus)] and Metasyrphus [=Eupeodes (Metasyrphus)]; in their tribe Syrphini.
Rotheray and Gilbert (1989) recovered Scaeva as sister group of Eupodes, and Eriozona as sister group of these two genera. In 1999, Scaeva was placed in a tritomy with Eupeodes and Ischiodon (Rotheray and Gilbert 1999).
Mengual et al. (2008) using molecular characters recovered Scaeva as monophyletic and sister group of Ischiodon (although they used the synonymy with Simosyrphus suggested by Laska et al. in 2006). Pseudodoros (Dioprosopa) was resolved as their sister group.
Flowers visited by adults: white umbellifers; Buxus, Erica, Hamamelis, Leontodon, Ligustrum,Origanum, Polygonum, Ranunculus, Salix, Sarrothamnus, Taraxacum, Tussilago, Viburnum opulus (Speight 2010).
Larvae of S. selenitica have been reported feeding on Adelgidae and Aphididae (Rojo et al. 2003).
Its flight period is from March to September over much of Europe, but from June to September in montane regions and cooler climatic zones. In central Europe, adults have been reported feeding at flowers in February (e.g. Schedl 1992), and although there do not seem to be unequivocal reports of adult flies of S. selenitica found hibernating it is almost certain that they do hibernate, probably at some height above the ground in chinks and crevices in bark of standing trees and in splits and cracks in broken branch ends attached to trees or similar splits and cracks in wooden beams of old farm out-buildings (Speight 2010).
This species ranges from Fennoscandia and the Faroes (Jensen, 2001) south to Iberia and the Mediterranean, including North of Africa; from Ireland eastwards through much of Europe into Turkey and European parts of Russia; from the Urals through Siberia to Cis-Baikal and on to Sakhalin and the Kuril Isles (Speight 2010). It has ben introduced in North Carolina (Thompson 210).
The preferred environment of S. selenitica is most types of deciduous forest, including scrub woodland and orchards, plus evergreen Quercus ilex forest in southern Europe (Speight 2010).
Adults inhabitat clearings, tracksides etc.; fast-flying, making a distinctive, high-pitched whine while investigating flowers etc.; usually flies within 3 m of ground; settles on foliage of bushes and shrubs in the evening, to sun itself; males hover at 2-4 m in clearings (Speight 2010).
Followin Speight (2010) the existing descriptions of the larva of this species all predate reinstatement of the closely similar S. dignota as a distinct (and widely distributed) European species, and could thus be based on either S. dignota or S. selenitica. But the description provided by Dixon (1960) has the virtue that it is based on material from part of Europe (Britain) where S. dignota does not seem to occur and can thus be presumed to refer to S. selenitica. Even though diagnostic features of the last instar larva and puparium of this species have more recently been given and figured by Laska et al. (2006), who also provide a key separating both its larvae and puparia from those of the other Scaeva species known from Europe, it is apparent that the developmental stages of S. dignota and S. selenitica remain virtually indistinguishable. Speight et al (1986) also figure features of the puparium. The larva is aphid feeding, on shrubs and trees; Kula (1982) reports larvae of this species as overwintering among leaf litter of the floor of spruce (Picea) forest.
Larva (from Dixon 1960).
Length 18-19 mm., width 4 mm., height 3-5 mm.; light green with a white median line of adipose tissue superimposed upon a broad median dark brown band, the white line interrupted by five transverse rows of orange-brown adipose tissue between dorsal segmental hairs on abdominal segments, aggregations of white adipose tissue forming flecks especially concentrated in dorsolateral prominences; subcylindrical, tapering anteriorly, cuspidate posteriorly; serrate in outline; ventral sole with seven segmentally arranged pairs of two prominences; integumentel vestiture of dense dark brown spinules; segmental ornamentation of long hairs mounted on individual papillae on slight prominences in ten rows of 12, 18, 16, 12, 12, 12, 12, 12, 12, and 2 respectively. Posterior respiratory process: recessed in a triangular depression where integumental vestiture is finer and denser; twice as broad as long; constricted at the base; median groove slightly less than half as deep as length of respiratory process; circular plates elongate oval, displaced towards the median groove and anteriorly; dorsal spurs prominent, pointed, and contiguous with inner and part of posterior border of circular plates; interspiracular ornamentation of small nodules; spiracles straight, equidistant and on slightly raised carinae; spiracles III parallel to median groove; spiracles with an inner border of hairs.
Larva (from Laska et al. 2006).
Immature stages previously described by Scott (1939), Brauns (1953), Dušek and Láska (1959), Dixon (1960) and Speight et al. (1986, only puparium). Larvae predatory on a wide range of aphids, prey records cited by Rojo et al. (2003, p. 202–204).
Diagnostic characters. The larva can present two patterns of colouration, green with a white median stripe (as in S. pyrastri) or brownish similar to Eupeodes spp. larvae. Body surface coated with well developed brown pigmented microtrichia about 0.03–0.045 mm long on dorsum. Dark segmental pattern on puparium present as dots arranged on dorsum, even if sometimes inconspicuous. Posterior folds coated with microtrichia with a wide base that becomes suddenly fine. Posterior respiratory process (PRP): (Width: 0.56–0.65 mm, height: 0.30–0.41 mm, n = 10). Short, pale brown in colour. Median groove deeper than half the length of PRP, in anterior view tips of dorsal spurs as wide apart as more than semi-diameter of spiracular plate. Ecdysial scars displaced towards median groove and anteriorly. Carinae I and II well developed with clear depression between them. Periorificial setae mounted inside of circular nodules, periorificial setae between orificia I and II close, with their nodules connected.
unless otherwise stated