Day 2 of my dragonfly species a day to celebrate the British Dragonfly Society’s National Dragonfly week. Today we’ll look at the Scarce emerald, Lestes Dryas
Like other emerald damselfly species they are emerald green in colour and they have a habit of sitting with their wings at 45 degrees to the body, rather than closed together as other damselflies do. The Scarce emerald has a more stocky or robust build than other species, which is often enough to separate them from them. To be sure of an ID, you need to separate them from the ‘common emerald’ (Lestes sponsa), which in males means you need to look at the second segment (from the front) of the abdomen (known as S2) which is totally covered in a blue powder colouring in the ‘common’ emerald (L. sponsa), but in scarce (L. dryas) is only half covered, as in the specimen below
The blue powder can come off, leading to some confusion between the two species, so to be certain you need to inspect the claspers at the tip of the abdomen, the internal set of which are broader and more inwardly curved in the scarce emerald.
In the UK the scarce emerald is restricted to sites near the Thames Estuary in Essex and Kent (and Greater London) and a few pingo pools in Norfolk. They prefer ponds and ditches with thick vegetation and little open water (Smallshire and Swash, 2004) and are usually found flying between rushes and reeds, rather than over open water. I have observed tandem pairs, like the those in the photo below, doing this and the male will land and then walk backwards down a reed/stem to move further into the cover.
They often found in temporary pools, which present a problem for an creature with aquatic larvae. They get round this by egg laying in the rushes and other plant stems above the falling (or dried up) water level and these eggs then overwinter, before hatching in spring after the pond has filled with the rain/melted snow of winter. These larvae then have time race against the falling water levels in spring and summer and emerge before water dries out completely. To do this they are more active and grow more rapidly than other larvae and are able to complete their larval stage in 8 weeks (Smallshire and Swash, 2004), much quicker than the typical 1 or 2 years of other species. I’ve found a few larva pond dipping in May and June.
The adults are on the wing typically from late June to end of July/ Mid-August, though a couple of years ago I found one on the last day of May and they were about in decent number at the end of August last year.
More on Dragonflies here: British dragonfly society
D. Smallshire and A. Swash, 2004, Britain’s Dragonflies, Wild Guides Ltd.