Common Blue Damselfly, Enallagma cyathigera
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Size
Small; body length 25mm to 30mm
Colour-patterning
Males share a very similar colour-patterning with the Azure Damselfly, Coenagrion puella, but, overall, appear slightly bluer. The blue stripes on the thorax behind the eyes are somewhat better developed and are separated from the blue sides of the thorax by a black bar which is narrower that the stripe itself opposite to the case in the Azure Damselfly. The second abdominal segment is characterised by a stalked ball (like a button mushroom) pattern. Both the eighth and ninth abdominal segments are entirely blue. Females have black abdomens with narrow dull greenish-blue bands and the stripes on the thorax behind the eyes are greenish-blue.
Behaviour
This is our most aggressive damselfly defending its territory from both its own kind and others. Paradoxically, populations of males often swarm out over expanses of water, flying only a few centimetres above the surface, as if with some common purpose. Similarly large numbers will shelter from the wind on favoured patches of vegetation, continually jostling for position. Mating takes place on vegetation and eggs are laid on submerged vegetation with the female often descending below the surface for up to half an hour.
Where to look for it
Generally this species can be found wherever there is fresh or brackish water as long as it is not fast flowing, but it shows a distinct preference for larger expanses of still water. It is not common in Plymouth and is only ever present in small numbers and should be looked for in the lower Plym Valley, Newnham Public Open Space, Efford Marsh and Forder Valley Local Nature Reserves.
Distribution and status
Uncommon in Plymouth with only small populations to be found at any given time.
When to look for it
Mid May to August.
Similar species
It is very easy to confuse with the Azure Damselfly, Coenagrion puella. However, males should be immediately distinguishable by the stalked ball shape on the second abdominal segment and the unpatterned eighth and ninth segments. Females can be best separated from the Azure Damselfly by the absence of a clear blue tenth abdominal segment.