Knowing that the abdomen of a damselfly consists of 10 segments, the Blue-tailed Damselfly (Ischnura elegans) can be distinguished from the similar looking Scarce Blue-tailed Damselfly (Ischnura pumilio) by having an entirely blue 8th segment while the Scarce Blue-tailed Damselfly has an entirely blue 9th segment.

Top: Siertuin Gooilust, 's Graveland, The Netherlands, 27 July 2016
Left: Zanderij Crailo, Hilversum, The Netherlands, 24 June 2013
Middle: A female. Spandersbos, Hilversum,The Netherlands, 22 July 2016
Right: Loosdrecht, The Netherlands, 10 July 2011
Last: Boekel area, The Netherlands, 6 July 2018