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.

Hortobágy-Halastó, Hortobágy National Park, Hungary, 2 May 2019