Keeled Skimmer, Orthetrum coerulescens
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Size
Medium sized; body length 25mm to 30mm.
Colour-patterning
Males are a very dark brown with upper surface of the abdomen a bright powder blue. There is a pair of dull yellow stripes on the thorax behind the eyes. Females
have lighter brown ground colouration than the males and range from a mid grey-brown in older specimens to a bright yellow-brown in young specimens. They also have a pair of dull yellow stripes on the thorax. Females lack the blue abdominal colours of the male but have a narrow black line running down the centre of the abdomen and a pair of similar lines edging the sides of the abdomen. The wings are lightly tinted amber throughout becoming more intense towards their bases.
Behaviour
A restless, active Skimmer, resting frequently on both standing vegetation and patches of bare ground, especially warm stones. At rest on the ground, the wings are held out flat at right angles to the body but, when resting on vegetation, the wings are commonly inclined forwards and downward in a very characteristic position. The males tend to be fairly tolerant of each other amongst denser vegetation but become more aggressive and territorial where the vegetation is sparse. Mating takes place amongst vegetation and the females lay their eggs whilst flying over water by dipping the tips of their abdomen into the water with each egg release.
Where to look for it
Open but sheltered ponds, bogs and slow moving streams. The only site where it known to occur in the city is privately owned but it should be looked for in the Wixenford and Saltram area.
Distribution and status
Very rare and restricted to a single known site in Plymouth where there is a strong breeding colony.
When to look for it
Early June to September.
Similar species
Males look similar to male Broad-bodied Chasers, Libellula depressa, and male Black-tailed Skimmers, Orthetrum cancellatum. However, they lack the robustness and yellow abdominal flank markings of the former and the darkened posterior half of the abdomen of the latter. Females are confusable with female Broad-bodied Chasers, Libellula depressa, Black-tailed Skimmers, Orthetrum cancellatum, and Common Darters, Sympetrum striolatum.
Female Black-tailed Skimmers and Common Darters, lack thoracic stripes and, together with females of the Broad-bodied Chasers, they all lack the dark line running down the middle of the abdomen.