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| Insects of Britain and Ireland: the genera of Syrphidae (hoverflies) |
Ascia
Adult flies. The flies sphecid wasp-like (cf. Stigmus solskyi and Crossocerus spp.); blackish, often marked yellowish or tawny; minute to small; 3–6 mm long. Wings 3–5.5 mm long.
The head wider than the thorax to about the same width as the thorax. The face entirely dark in ground colour; flat or concave in the region between the antennae and the mouth; without a central knob; produced below and extending beyond the antennae, or not extending below beyond the antennae. Antennae relatively short, drooping; with their bases approximated, or with their bases well separated; black, or black and red. 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. The scutellum black. Wings patterned to plain (slightly grey, with (e.g., N. podagrica) or without (e.g., N. tenur) a brown band from mid-costa to the disc and brown clouding of apical transverse veins); 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; bent at a sharp angle to 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 wider than the thorax to narrower than the thorax (wider in the females); clavate (heavily so in females); proximally petiolated (more or less so, in females), or not petiolated. The male abdomen with 4 visible segments. The abdomen contrastingly patterned (but sometimes colour-tailed only). The tergite patterning involving 2 and 3. The colour-patterned tergites marked with yellow, or tawny. The interrupted band on tergite 2 reduced to small paired spots, or not reduced to small spots. The tergite bands medianly interrupted, or entire, or medianly interrupted and entire, or partially interrupted and entire; narrow. The spiracles of the third abdominal segment borne at or near the anterior corner of each side.
Larvae and pupae. The larvae to about 6 mm long, tapering posteriorly; tailed. The anal segment tapered gradually to the spiracular process; shorter than the rest of the body (not rat-tailed). The larvae dorso-ventrally flattened (with small prolegs); brown, plain; with hooks on the thorax (a single pair oat the anterior margin of the prothorax, directed backwards), or without thoracic hooks; mouth without triangular sclerites; anal segments with lappets. The larvae aquatic to non-aquatic; saprophagous, or coprophagous (found in decaying vegetation around ponds and in farmyard manure), or phytophagous (? - being also recorded from Petasites petioles).
General comments. The adults with a concave face leading smoothly to the projecting margin of the mouth, and a thickened hind femur.
Classification. Subfamily Milesiinae; tribe Chrysogastrini.
British representation. 6 species in Britain.
Illustrations. • N. dispar, N. podagrica: Verrall. • 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. • N. podagrica, with assorted other Syrphidae (adult forms). Syrphidae. 1, Baccha elongata, female; 2, Neoascia podagrica, male; 3 and 4, Melanostoma scalare, male and female respectively; 5, Syritta pipiens, male; 6, Tropidia scita, male; 7 and 8, Sphaerophoria scripta, male and female respectively; 9, Sericomyia silentis, male; 10, Xylota segnis, male; 11, Rhingia camprestris, female; 12, Eupeodes luniger, male; 13, Episyrphus balteatus, female; 14, Helophilus transfugus L., female (= ?); 15, Chrysotoxum cautum, male; 16, Eristalis arbustorum, male. Adapted from C.O. Hammond (Colyer and Hammond, 1968).
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’.
