Insects of Britain and Ireland: the genera of Syrphidae (hoverflies)

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L. Watson and M. J. Dallwitz

Scaeva Fabricius

Catabomba Osten Sacken, Lasiopthicus; formerly Syrphus p.p.

Adult flies. The flies somewhat Nomada-like, or vespid wasp-like (but cf. also the mainland-european crabronid Bembix rostrata); black marked with whitish or yellow; small to medium sized; 10–15.9 mm long. Wings 8.5–12.5 mm long.

The head wider than the thorax. The face ground-coloured at least part yellow; not flat or retreating between antennae and mouth; with a central knob to without a central knob; not elongated horizontally into a cone as long as the rest of the head. The frons markedly inflated (usually), or not inflated (in S. mecogramma); smooth. The eyes hairy. Antennae relatively short, drooping; with their bases well separated; black and tawny. The third antennal segment ovoid or orbicular. The antennal bristle dorsal; simple (bare).

The humeri bare. The thorax pubescent without stiff bristles interspersed; plain. The scutellum at least partly yellow, or brownish, ferrugineous or tawny. Wings plain (colourless); without a conspicuously dark stigma; without black flecks along the hind edges; divergent 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 (though downwardly curved); without a backwardly projecting, incomplete transverse veinlet. The lower outer marginal vein more or less parallel with the posterior wing margin. The upper and lower outer marginal cross veins more or less continuous to slightly stepped. The upper outer marginal cross-vein conspicuously bent near the base the base; re-entrant to not re-entrant. The alula distinct. The thoracic squamae without long hairs dorsally. The hind legs partly yellow. The anterior anepisternum bare.

The abdomen wider than the thorax; depressed, broadly obovate, or oval. The lateral margins of the tergites exhibiting beaded rims. The abdomen with 5–6 segments apparent. The male abdomen with 5 visible segments. The abdomen contrastingly patterned (usually, with lunules), or not contrastingly patterned (sometimes melanic). The tergite patterning involving 2 to 4. The colour-patterned tergites marked with whitish to yellow. The dorsum of tergite 2 with golf-club shaped spots, or without golf-club shaped spots; exhibiting a wineglass-shaped black area, or without a wineglass-shaped black area. The dorsum of tergite 3 with a pair of pale marks in the form of a moustache, or not marked in the form of a moustache. The tergite bands medianly interrupted; relatively narrow. The spiracles of the third abdominal segment borne in the middle of each side.

Larvae and pupae. The larvae broader posteriorly, tapered to the head; posteriorly blunt and tail-less; scarcely flattened (sub-cylinfrical); green, or not green; longitudinally striped (with broad dorsal and narrow lateral pale stripes); patterned (green, brown or pinkish); mouth with a triangular sclerite on either side; anal segments without lappets. The larvae predatory (aphidivorous: S. pyrastri on a wide range of ground layer and arboreal species, S. selentica associated with pines).

General comments. The adult abdomen is characteristic, with the lunules sharply incurved anteriorly at the median line..

Classification. Subfamily Syrphinae; tribe Syrphini.

British representation. 4 species in Britain.

Illustrations. • Scaeva pyrastri (Concolourous Hover-fly: B. Ent. 509). • Scaeva pyrastri: B. Ent. 509, legend+text. • Scaeva pyrastri: B. Ent. 509, text cont.. • S. pyrastri, S. selenitica: Verrall. • 18 genera (from Walker). • S. pyrastri, female (with Syrphus, Helophilus and Xanthogramma).

To view the illustrations with detailed captions, go to the interactive key. This also offers 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.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. Insects of Britain and Ireland: the genera of Syrphidae (hoverflies). Version: 28th July 2015.’.