| Keeled Skimmer (Orthetrum coerulescens (Fabricius, 1798)) |
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Scientific name: Orthetrum coerulescens (Fabricius, 1798) Common name: Keeled Skimmer French name: Orthetrum bleuissant Order: Odonata Suborder: Anisoptera Family: Libellulidae Wingspan: 57 to 63 mm. Biotope: Running water of different sizes, from large rivers to small brooks. Geographic area: North Africa and surroundings of the Mediterranean sea, Europe north to southern Scandinavia and east to the Russian border. Flight time: April to November with a peak in summer. |
The Keeled Skimmer has brown or yellowish pterostigmas which differentiate it from the Black-tailed Skimmer and from the White-tailed Skimmer which have black pterostigmas (these last species are also a larger size). Males have a brown thorax with whitish antehumeral stripes which disappear with age. The abdomen becomes blue on mature males. The front of the head is a dark greyish brown colour. This allows to tell it apart from the Southern Skimmer (Orthetrum brunneum) which shows a much more pale face. The Keeled Skimmer's pterostigmas are also much longer than the Southern Skimmer's ones. In case of a doubt you need to have a close look at the veins on the wings. In particular at the number of split cells under vein IR3 (4 to 9 on Orthetrum brunneum, less than 4 on Orthetrum coerulescens). Females have a dark brown thorax with whitish antehumeral stripes. The abdomen is yellowish brown with a thin black longitudinal line on the top and a small black cross bar at the back of each segment. There is a possible confusion with a female Broad Scarlet (Crocothemis erythraea). You can recognize this last one with the yellow area at the base of the wings. This area is clear on Orthetrum coerulescens. There is also a possible confusion with some members of the Sympetrum genus like the Southern Darter. The members of the Orthetrum genus show a larger number of antenodal veins (small transverse veins on the costal edge between base and nodus), that's to say respectively more than 8 and more than 6 on the fore wings and on the hind wings while Sympetrum species show 6 to 8 and 5 to 6. |
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I have initially searched among sympetrum species because of the size and because of the other species usually observed at the same place. So I have thought to a female Southern Darter (Sympetrum meridionale) despite the presence of black marks on the abdomen. I have found this was an error while I was reading the Orthetrum pages in my dragonfly guide. The length of the pterostigmas and the whitish antehumeral stripes allow to discard the Southern Skimmer species. The clear base of the wings allows to discard a female Crocothemis erythraea. |
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Here is another picture erroneously listed before as Southern Darter (maybe because of the name of the species and the southern location where the picture was shot). I have been able to detect and correct my error with a closer exam of the antenodal veins. |
André Bon July 2017