~ Willow Emerald ~

Willow Emerald - Chalcolestes viridis


A large, metallic, olive-green damselfly that - like the other emerald species- has the unusual trait among damselflies of perching with it's wings half open. It often rests quite high up on trees (especially willow) that overhang slow-flowing rivers. As such, the abundance of willows overhanging the River Yare at UEA provides abundant habitat for this species. 
Interestingly, this species is a very recent colonist to the UK, and still considered very scarce in the UK as a whole. It was first recorded in the UK in 2007 and has since spread well across East Anglia. New sites are being found each year, and so it seems likely this species will continue to spread further west.

Mating Willow Emeralds

Unlike other damselfly species that lay their eggs in water, this species lays their eggs in the branches of trees that overhang water. The eggs stay in the branches until next spring when they hatch and the prolarva then fall into the water where they rapidly grow and in a space of a few months, emerge as adults.

Identification is relatively straight forward as there is little overlap between this species of emerald and others. To conclusively ID however, look on the side of the thorax for a prominent spur (shown below). The cream/pale-brown pterostigma (the coloured section on the outer edge of the wing) is also a good feature look out for. They are a late species to emerge (usually around mid-late August) and can be found right until the end of October (even into the first week of November if conditions are right), so there is still plenty of time to go and search for them.

Characteristic 'spur' marking on thorax

They appear fairly widespread at UEA, though hotspots seem to be in the trees/hedges along the western edge of the broad, and along the stretch of river that runs to the south of the broad, up until the boardwalk at the eastern end.