Dragonfly Guide

Ischnura saharensis

Aguesse, 1958

Sahara bluetail

Ischnura saharensis
Ischnura saharensis, male. Las Palmas, Spain. 2016.
Photo: Paul CoolsCreative Commons CCCreative Commons BY

Description

This close relative of I. elegans is endemic to the western Sahara and the Canary Islands. It may be differentiated from I. graelsii by the green thorax, and from I. fountaineae by its smaller size, although only by certainty by the male's appendages. Females may be inseparable in the field.

Mature males are similar to I. elegans byt with a green colouration of the head, thorax and abdomen base. Blue individuals are likely the blue colour form of the female or coexisting I. graelsii or I. fountaineae. The underside of S3-7 in males is more vividly orange than in other species except I. fountaineae.

Unlike I. graelsii and I. fountaineae the upperside of S8 in females is never marked with black.

In both sexes the postocular spots tend to be small and the antehumeral stripes are narrow, but this is similar to I. graelsii and I. fountaineae.

Spring generation is particularly dark, with reduced postocular spots and antehumeral stripes. Female variation and development is not fully understood. Form C is most frequent, and has a pink thorax first and large postocular spots, becomming greenish and finally brown. Form B is similar when mature, but the immature colour is unknown. Andromorph A-females may have either a bright green or a bright blue thorax.

Behaviour

Several generations throughout the year, although scarce from December to February.

Distribution

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Distribution map. Data from gbif.org

I. saharensis is found throughout a large part of the Sahara west of Egypt and Sudan. It reaches the Mediterranean coast in south-western Morocco and in the western Sahara, with the westernmost occurrences in the Canary Islands. It is replaced by I. senegalensis in the east and south of its range and by I. graelsii in the north, being sympatric and even synoptic with these species only locally in the Maghreb, the Canary Islands and Mauritania.

I. saharensis is in Europe only known from the Canary Islands, but old records of "Agrion maderae" and I. senegalensis from the MAdeira archipelago probably also refer to this species. It is common and widespread in the Canary archipelago, with over 20 localities distributed among all islands with the exception of Hierro.

Habitat

I. saharensis is found at all kinds of standing and running waters in desert and semi-desert areas, including ditches, rivers, ponds and lakes with fresh or brackish, permanent or ephemeral waters. This species is well adapted to arid environments, as it is salt-tolerant and highly mobile. It is known to readily colonise newly available habitats, and its rapid larval development allows it to reproduce successfully in areas where a large portion of the available aquatic habitats consist of ephemeral water bodies flooded only during the rain season.

Sources

  • Atlas of the European Dragonflies and Damselflies, Jean-Pierre Boudot(Editor), Vincent J Kalkman(Editor), Fons Peels(Illustrator)

  • Dragonflies and Damselflies of Europe: A scientific approach to the identification of European Odonata without capture, Galliani, C.; Scherini, R.; Piglia, A.

  • Field guide to the dragonflies of Britain and Europe, Klaas-Douwe B Dijkstra.