British Insects: the Odonata
Common Blue Damselfly.
Adults. Adults about 29–32–35 mm long. Average wingspan 38 mm; hindwings 18–20 mm long.
The eyes lateral and widely separated; brown, or brown and green (in the female), or blue (in the male). The front of the head immediately interior to the eyes pale whitish blue.
Legs black and blue (greenish blue below). Thoracic antehumeral stripes present (the humeral stripes also conspicuous); blue (in the male), or green (in the female). The wings held vertically in repose; similar in shape and venation; petiolate; unpatterned and clear. The inner wing venation blackish. Discoidal cell a simple quadrilateral, not longitudinally divided (trapezoid, without transverse veinlets). The wings exhibiting 3 postquadrilateral cells between the quadrilateral cell and the subnodus. Antenodal veins in the forewings 2. Pterostigma elongated but only about about twice as long as wide (diamond shaped); black. The hindwings with two rows of cells distal to the pterostigma between the costa and the radial vein.
Abdomen linear from base to tip (very slender); 24–28 mm long; predominantly blue and black (in the male and some females), or green and black (in other females); in the male, segment 2 is complexly patterned, while all the others but 8 and 9 are entirely or posteriorly black; while in the female, the abdomen is mostly dorsally black, with each segment green or blue anteriorly and on the sides; without mid-dorsal spots. The male abdomen without auricles on segment 2; with paired inferior anal appendages. Abdominal segment 8 of the female with a ventral apical spine (this strong).
Nymphs. The nymphs elongate and slender-bodied, gradually tapering posteriorly; when mature, 20–26.5 mm long.
The head without prominent spots. The antennae with the scape considerably shorter than the other segments taken together; with the first flagellar segment longer than the pedicel. The mask narrowed gradually to the hinge; without a median cleft. The prementum bearing 6–10 major setae (3+3 to 5+5). The body of the labial palps bearing 6–7 major setae. The outer margins of the labial palps without spines. Distal margins of the labial palps crenate and coarsely toothed. The moveable hooks of the labial palps without setae. The apical combs of the tibiae mainly of trifurcated setae.
The abdomen terminating in three conspicuous caudal gills. The three caudal appendages all lamellar. The caudal lamellae (elongate-) oval; pointed (not apiculate); usually with transverse dark bands (these one to three, narrow); hairy on both margins to beyond the middle; nodate, with the marginal hairs coarser proximally to the node and finer beyond it; with much-branched primary tracheal branches leaving the main trunk at an upward angle. The gizzard with 8–16 radially symmetrical folds.
Distribution. Northern Scotland, southern Scotland, northern England, English Midlands, East Anglia, Wales, southeast England, southwest England, Isle of Wight, Ireland, and central southern England (very widespread and usually common). Adults on the wing late April to early October (generally in best mature condition late May to mid-September).
Classification. Zygoptera; family Coenagriidae.
General comments. Hindwing generally with two rows of cells between the costa and the radius distal to the pterostigma.
Illustrations. • Enallagma cyathigerum (from Lucas). • Enallagma cyathigerum, nymph dissections (Lucas). • Pyrrhosoma and Ceriagrion? (from Shaw and Nodder, about 1801).
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. British insects: Dragonglies and Damselflies (Odonata). Version: 1st January 2012. http://delta-intkey.com’.