The Willow Emerald Damselfly – Chalcolestes viridis, is a recent addition to the County list. Easily missed owing to its resemblance to to the Emerald Damselfly – Lestes sponsa, and its habit of resting in trees close to the water’s edge.
The largest damselfly in the region, apart from the Banded demoiselle – Calpoteryx splendens. Noticeably larger than the blue damselflies and characteristically rests with wings held half open at 45° or wider.
Males and females share similar colouring, with the upper surfaces of the thorax and abdomen being predominantly metallic green, and the lower surfaces a pale creamy-brown. Males lack the blue pruinescence found in the Emerald Damselfly.
Overall length: 39 – 48 mm
Wings: 23 – 28 mm
Emerald damselfly species are very similar, but in Bedfordshire this is mostly likely mistaken for the Emerald Damselfly – Lestes sponsa, particularly females. The Willow Emerald is a little larger, and emerges later in the year.
Careful examination of the thorax, pterostigma, and (male) claspers separates the two species, differences are summarised below:
|Feature||Willow Emerald Damselfly – |
|Emerald Damselfly – |
|Thorax||Upper (dark green) and lower (light green) surfaces. The darker area extends into the lighter with a noticeable ‘spur’, giving it a zig-zagged appearance||Upper (dark green) and lower (light green) surfaces with a straighter delineation between the two|
|Pterostigma||Pale, with obvious border||Dark brown|
|Abdomen: Male||All green, without pruinescence||S1, S2, S9, & S10 with light blue pruinescence|
|Abdomen: Female||S1 has a single unbroken dark green area, giving the appearance of a solid ‘m’ or sideways ‘B’ shape||S1 has two dark green quadrant shaped markings, separate from each other|
|Claspers||Pale, straighter upper appendages, lower appendages short and barely visible||Dark, upper appendages noticeably curved, long lower appendages|
|Flight period||July – October||June – September|
Favours shallow still water sites, ponds, ditches etc., and slow rivers. Often encountered away from water, but careful searching can find them in trees overhanging water.
A recent colonist in Bedfordshire, not common but can be be locally abundant at some sites like Felmersham NR. Also recorded at Priory CP, Marston Vale CP, Duck End NR.
Visible between early July and October, peaking in August and September – a little later than the Emerald Damselfly – Lestes sponsa.