British Insects: the Odonata
Scarce Blue-tailed Damselfly.
Adults. Adults about 26–29–32 mm long. Average wingspan 33 mm; hindwings 14–18 mm long.
The eyes lateral and widely separated; black and blue (usually dark, with a circular blue spot at the rear, in both sexes). The front of the head immediately interior to the eyes pale whitish blue.
Legs pale, with a black streak. Hind tibia without a featherlike expansion. Thoracic antehumeral stripes present (usually, and with humeral stripes also visible), or absent (in f. aurantiaca, with an orange thorax); blue, or green. The wings held vertically in repose; similar in shape and venation; petiolate; unpatterned and clear. The inner wing venation brown, or brown and blackish (in f. aurantiaca). 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 more or less isodiametric (rectangular or trapezoid, much larger on the forewings than the hindwings); light brown to yellow, or pale with a dark centre (yellowish, often dark brown internally on the forewings of the male). The hindwings with only one row of cells distal to the pterostigma between the costa and the radial vein.
Abdomen linear from base to tip, or linear from base to tip to linear from a conspicuously swollen base (slender); 22–25 mm long; predominantly blackish bronze, or black (marked with narrow intersegmental yellow bands in both sexes, and posteriorly with blue in the male); predominantly transversely banded (with thin yellow intersegmental bands, and segments 8 posteriorly and 9 entirely blue in the male); 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 small).
Nymphs. The nymphs elongate and slender-bodied, gradually tapering posteriorly; when mature, 15–20 mm long.
The head in dorsal view markedly narrowing from immediately behind the eyes. The postocular lobes curving sharply to the back of the head from some distance behind the eyes. 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 12 major setae (6+6). The body of the labial palps bearing 5 major setae. The outer margins of the labial palps without spines. 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 more or less oval (less obviously tapered towards the apex than in L. dryas); quite blunt tipped; hyaline without coloured markings; with one margin hairless beyond the middle, the other hairy to nearer the apex (? - Gardners Fig. 10f, labelled I. elgans, contradicts his generic key); 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. Wales, southeast England, southwest England, Ireland, and central southern England. Adults on the wing late may to early September (generally in best mature condition mid-June to mid-August).
Classification. Zygoptera; family Coenagriidae.
Illustrations. • Ischnura pumilio and I. elegans (from Lucas).
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’.