I was originally not a great fan of the term Bluet [seems too American] but it is succinct when it comes to encompassing two genera (Coenagrion & Enallagma); Blue-striped Damselflies is a bit of an ungainly mouthful.
The UK is home to seven Bluet species, one Enallagma and six Coenagrions. Four of the Coenagrions have very restricted/localized ranges, however:
- Irish Damselfly (C. lunulatum) – Ireland only;
- Northern Damselfly (C. hastulatum) – eastern central Scotland only;
- Southern Damselfly (C. mercuriale) – mainly Hampshire, with the southwest and southern Wales;
- Dainty Damselfly (C. scitulum) – one or two private sites in northern Kent.
So the majority of areas in the UK need be concerned with only three potentially confusing species.
My nearly all-encompassing comparison chart includes the males, the blue-and-black guys, of the five GB Coenagrions [I am yet to find C. lunulatum, the Irish Damselfly] together with the Enallagma.
“Why have you said colour?”, I hear you ask. Many people have been confused by the fact that immature males are not yet blue but more of a beige or grey colour. Looking in a field guide, one finds nothing that looks right. The black pattern, however, is developed and identification is still possible if you ignore the colour. So, weird though it may seem, I produced a monochrome comparison to try and force people to ignore the (lack of) colour.
To avoid the what to most people is the unnecessary clutter of the four restricted species, I have a few more specific comparisons. The really widespread species are two, the Common Blue Damselfly (Enallagma cyathigerum) and the Azure Damselfly (Coenagrion puella).
The Variable Damselfly (C. pulchellum) is widespread in Ireland and parts of England, where populations are more scattered. Southeast Scotland also has populations. It is very closely related to the Azure Damselfly (C. puella). The females are particularly challenging.
And so to the tricky subject of females [keep your comments to yourselves]. Female Coenagrions are particularly tricky since their patterns are all but identical, for many. This is particularly true of the “terrible twins”, Azure (C. puella) and Variable (C. pulchellum). The only sure way to identify them is the shape of the trailing edge of the pronotum, the plate covering the prothorax, to which the front pair of legs is attached. For the sake of comparison, I have included the female Common Blue (E. cyathigerum). There’s also a more detailed look at the female Azure and Variable pronotums, and an example of the variation possible in male S2 markings.
- Comparison: GB Bluets (female)
- Comparison: Female Azure vs Variable Pronotums
- Azure male S2 variation