Bulletin 38 - July 1989: Odonata of Das Island



Odonata of Das Island

by D.C. Heath

Das Island is situated in the Arabian Gulf approximately 104 miles NW of Abu Dhabi town. The island is host to a variety of passing wildlife including species of the Order Odonata (dragonflies and damselflies).

Dragonflies are relatively large and robust and belong to the sub order Anisoptera, whilst the slender and smaller damselflies belong to the sub order Zygoptera. Probably the easiest way to differentiate between the two is to observe them when not flying. Dragonflies settle with wings outstretched whereas damselflies settle with wings folded over their body (except those of the Lestes family, which settle with wings half-folded). Generally speaking, there are two kinds of dragonfly, the hawkers and the darters. Darters normally rest on vegetation and when a likely meal passes by they dart out and capture it. Hawkers patrol a stretch of vegetation, stream or pond, ready to take their prey on the wing. Observation suggested three different species of dragonfly on Das Island.

One day in June 1988 I found one in its death throes, and within minutes of picking it up it had died, so I decided to keep it for identification purposes. Unfortunately, soon after death Odonata lose their colour, making identification of dead specimens quite difficult. However, they can still be identified by the pattern and number of wing veins, plus details of genitalia. A few days later another dead specimen was brought to me and this was duly placed in a tobacco tin along with the first. A live specimen was next brought to me in a plastic bag, clearly none too happy at its captivity. I did not wish to kill it because it was such a healthy specimen and also it was the only one of that particular species that I had observed on the island. I therefore measured it as accurately as possible, did a coloured drawing and then released it back into the wild.

The dragonflies on Das are migratory, since there are no areas of open water on the island for them to breed in. Fresh water here is stored in covered tanks of various kinds, so the dragonflies must have arrived from one of the surrounding Gulf countries. While out fishing on a boat up to two miles off Das, dragonflies have on occasion alighted on board before flying on to the island. In August 1988, I took the dead specimens and drawing to the UK on leave and sent the package to the British Dragonfly Society, where Mr. Stephen Brooks, an entomologist at the British Museum (Natural History) examined them. The larger of the dead specimens was identified as the Globe Skimmer Pantala flavescens (Fabricius) which is so successful as a migrant that it is found throughout the tropical regions and is probably the commonest dragonfly in the world. Its general body colour is reddish brown, and the wings have red to brown pterostigma (see diagram), the one on the forewing being longer than that on the hind wing; the membranule is white. The abdomen tapers evenly from base to tip and is normally yellowish or reddish. Average measurements for male and female abdomen are 26-32 mm and hind wings 38-42 mm. The larvae of this species grows rapidly which allows for development in temporary pools of water.

Selysiothemis nigra (Vander Linden) was the smaller of the two dead specimens. This particular genus of dragonflies has a small number of species. S. nigra can be variable in body colour according to age and sex but is normally yellowish to blackish. Its wings are completely transparent with a short pterostigma 2 mm long. The female can lay up to 600 eggs and this species can travel long distances. Average measurements are:

male: abdomen 20 - 25 mm; hind wing 25 - 29 mm.
female: abdomen 18 - 21 mm; hind wing 24 - 28 mm.

The drawing I made was identified as Anax parthenope (Selys). The male abdomen is olive brown with a wide dark brown to black dorsal line, with the second and part of the third segment light blue. The female abdomen is olive brown with a black dorsal line and sometimes segments two and three are light blue in older individuals. Average measurements are:

male: abdomen 46 - 52 mm; hind wing 44 - 50 mm.
female: abdomen 49 - 53 mm; hind wing 47 - 51 mm.

These three specimens can be found in The Dragonflies of Europe by R.R. Askew, published by Harley Books, and in The Dragonflies of Britain, Europe and North Africa by J. d'Aguilar, J.L. Doromanget and R. Prechac.






 


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