One species not yet covered, the Scarce Blue-tailed Damselfly (Ischnura pumilio), is a bit awkward because the males have postocular spots and a tail light but the females have neither. So, let’s deal with the male now. 😉
The tail light of the male Scarce Blue-tailed Damselfly (Ischnura pumilio) is shifted rearwards compared to the Blue-tailed Damselfly (Ishnura elegans), being on the posterior ⅓rd of S8 (rather than the whole of S8) and S9. S9 has a variable amount of small black markings, too.
Tail light on posterior ⅓rd S8 & S9
NO tail light on posterior ⅓rd S8 & S9