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| Insects of Britain and Ireland: the genera of Syrphidae (hoverflies) |
Adult flies. The flies sphecid wasp-like (cf. Pemphredon and Psenulus); dark or blackish, sometimes marked yellowish to reddish; minute to small; slender, elongate, 5–9 mm long. Wings 4.75–7 mm long.
The head wider than the thorax to about the same width as the thorax. The face without a central knob. The eyes depicted as bare. Antennae relatively short, drooping; black, or tawny. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; simple (bare).
The humeri hairy, and readily visible behind the head. The thorax plain; without longitudinal stripes. Wings plain (slightly grey in S. clunipes); without a conspicuously dark stigma; incumbent and almost parallel in repose. Wing veins R2+3 and R4+5 not forming a closed cell. The anterior cross vein R-M in cell R5 crossing it before the middle of the adjoining discal cell. Vein R4+5 without a conspicuous curve projecting into the cell R5; without a backwardly projecting, incomplete transverse veinlet. Vein R without bristles. The lower outer marginal vein markedly diverging from the posterior wing margin. The upper and lower outer marginal cross veins strongly stepped. The upper outer marginal cross-vein conspicuously bent well above the base; curved on the bend; joining vein R4+5 almost at right angles, so that cell R5 is not extended towards the wing tip; not re-entrant. The alula indistinct.
The abdomen at the widest (posterior) part about the same width as the thorax, or narrower than the thorax; clavate; conspicuously proximally petiolated (segment 2 being narrow-elongate, with 3 and 4 broadened); contrastingly patterned (in males), or not contrastingly patterned. The tergite patterning involving 3 (only), or 3 and 4. The colour-patterned tergites marked with yellow to tawny (to reddish?). The tergite bands entire; wide.
Larvae and pupae. The larvae tapering posteriorly; shortly tailed. The anal segment tapered gradually to the spiracular process. The larvae dorso-ventrally flattened (6–8 mm long, with small prolegs); pale brown, plain; without thoracic hooks; mouth without triangular sclerites; anal segments with lappets. The larvae saprophagous; in sap runs and in decaying sap under loose bark.
General comments. The adults with a concave face leading smoothly to the projecting margin of the mouth.
Classification. Subfamily Milesiinae; tribe Chrysogastrini.
British representation. 4 species in Britain.
Illustrations. • 18 genera (from Walker). 1, Chrysotoxum cautum, male: head (1a) and abdomen (1b) from the side. 2, "Psarus abdominalis" (not British?), side view of head (2a), and antenna (2b). 3, Paragus haemorrhous, male: head from above (3a) and side (3b), and tip of wing (3c). 4, Psilota anthracina: head from side (4a), and wing (4b). 5a, Pipiza noctiluca: head from the side. 6a, Orthoneura elegans: antenna. 7a-b, Chrysogaster cemiteriorum: head from the side (7a), and wing tip (7b). 7c, "Chrysogaster nigricollis" (= ?), wing tip. 8, "Brachyopa conica" (not British?), with head in side view (8a). 9, Rhingia rostrata: male head from above (9a) and from the side (9b). 10, Ferdinandea cuprea, with (10a) details of labrum and lingua showing one maxilla and its palp. 11a, Cheilosia illustrata: male head from the side. 11b and 11c, Cheilosia leucorum: proboscis (11b) and wing tip (11c). 12, Scaeva pyrastri, female, and (12a) head of male. 13a, Doros profuges: 8-jointed female abdomen. 14, Sphaerophoria interrupta, male, with extremity of the abdomen (14a); 14b, Sphaerophoria interrupta, abdomen of female. 15a and 15b, Baccha elongata: abdomen and hind leg. 16, Sphegina clunipes. 17a and 17b, Neoascia podagrica: head from the side, and wing tip. [18, Physocephala rufipes (Conopidae), and details of head from the side (18a), proboscis (18b), and antenna (18c)]. From Walker (1851, Plate X), with approximate lengths (head to abdominal tip) indicated.
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa. See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. Insects of Britain and Ireland: the genera of Syrphidae (hoverflies). Version: 27th July 2019. delta-intkey.com’.
