The UK is home to four Emerald Damselfly/Spreadwing species:
- Lestes sponsa (Common Spreadwing/Emerald Damselfly)
- Lestes dryas (Robust Spreadwing/Scarce Emerald)
- Lestes barbarus (Migrant Spreadwing/Southern Emerald)
- Chalcolestes viridis (Western Willow Spreadwing/Willow Emerald)
Only one is particularly widespread, the Emerald Damselfly (Lestes sponsa), though the Willow Emerald/Western Willow Spreadwing (Chalcolestes viridis), which began colonizing the UK in 2009, is spreading very successfully from its initial bridgehead near Ipswich, Suffolk and is becoming more widespread. You have to go looking for the other two. 😉
I have a chart comparing both male and female features of all four.
Though L. dryas is not particularly widespread, it can co-exist with L. sponsa (at Thompson Common in Norfolk, for example) and differentiating females of L. sponsa and L. dryas can be tricky, I also have a chart specifically comparing L. sponsa and L. dryas females.