The Small Spreadwing (Lestes virens) is a species of damselfly in the family Lestidae, the Spreadwings.
Spreadwings hold their wings at about 45 degrees to the body when resting. 
This distinguishes them from most other species of damselflies which hold the wings along, and parallel to, the body when at rest.
The Small Spreadwing can be distinguised from the other Spreadwings (Lestes species) by looking at the back of the eyes (head): the top half of the back is dark and the bottom half is yellow.
In addition, adult Small Spreadwings can be distinguished from the other Lestes species by their light brown pterostigma (wingspots) with clear light borders.
Adult males show blue at the end of their bodies (S9 and S10) but not at the base (S1 and S2) as in the Common Spreadwing (Lestes sponsa) and Emerald Spreadwing (Lestes dryas). 
And finally, a very good way to distinguish the Small Spreadwing from the Common Spreadwing (especially in females) is to look at the side of the first segment of the abdomen (S1).
The Small Spreadwing shows here a small dark spot (in Dutch: the "Neijtsvlek") whereas the Common Spreadwing doesn't.

Mila 23 area, Danube Delta, Romania, 24 May 2018