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| Insects of Britain and Ireland: the genera of Syrphidae (hoverflies) |
Orthoneura
Adult flies. The flies metallic blackish to greenish bronze; minute to small; about 4–7 mm long. Wings 4–6.25 mm long.
The head slightly wider than the thorax to about the same width as the thorax. The face without a central knob; almost produced below and extending beyond the antennae, or not extending below beyond the antennae; not elongated horizontally into a cone as long as the rest of the head. Antennae relatively short, drooping; with their bases well separated (on a tubercle); black, or ferruginous. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; simple (bare).
The humeri hairy, and readily visible behind the head. The thorax pubescent without stiff bristles interspersed; patterned to plain; with longitudinal stripes (with two longitudinal dust stripes on the dorsum), or without longitudinal stripes. The scutellum black, or aeneous. Wings patterned to plain (slightly grey, sometimes clouded dark in the disc); with a conspicuous 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. 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; re-entrant (e.g., O. nobilis), or not re-entrant. The alula distinct to indistinct.
The abdomen much wider than the thorax; depressed, broadly to narrowly oval, or ovate, or oblong. The male abdomen with 4 visible segments. The abdomen not contrastingly patterned. Tergites 2–4 dulled dorsally. The spiracles of the third abdominal segment borne at or near the anterior corner of each side.
Larvae and pupae. The larvae tapering posteriorly; tailed. The anal segment tapered gradually to the spiracular process; shorter than the rest of the body. The larvae scarcely flattened; dark brown, plain; without thoracic hooks; mouth without triangular sclerites; anal segments with lappets. The larvae more or less aquatic; saprophagous; in decaying vegetation (and mud, in still and slow-moving water).
General comments. The adults with a concave face leading smoothly to the projecting margin of the mouth.
Classification. Subfamily Milesiinae; tribe Chrysogastrini.
British representation. 3 species in Britain.
Illustrations. • O. brevicornis and O. nobilis: Verrall. • 15 genera (from Walker). 1, Ceriana conopsoides (adventive?), head in side view and extremity of wing. 2, Callicera aurata, with detail of antenna. 3, Microdon mutabilis, antenna and wing. 4, Eumerus strigatus, head in side view and wing. 5, Eristalis tenax: male head from above (5a), female head from the side (5b), and wing of female (5c). 6, Helophilus pendulus: head of male from above (6a) and from the side (6b), and extremity of wing (6c). 7, Merodon clavipes (extinct in Britain): head in side view, and hind leg of male. 8, Tropidia scita, male: head and extremity of wing. 9, Syritta pipiens, male, with head in side view (9a). 10, Xylota sylvarum, male: head (10a), antenna (10b), and base of hind leg showing coxa with a small spine (10d). 11, "Milesia speciosa" (Caliprobola speciosa?): head in side view (11a), wing extremity (11b), and base of hind leg (11c). 12, Criorhina berberina, with side view of head. 13, Volucella bombylans: side view of head (13a), antenna (13b), and wing extremity (13c). 14, Sericomyia silentis, with head from side (14a) and claw joint of tarsus (14b). 15, Orthoneura nobilis. From Walker (1851, Plate IX), with approximate lengths (head to abdominal tip) indicated. • 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’.
