Azure (Coenagrion puella) and Variable Damselflies (C. pulchellum) are the Terrible Twins, the females being pretty potentially identical from a point of view of markings. I say “potentially” because:
- whilst Azures generally do not have an inter-ocular bar, they occasionally do;
- Variables most often do have an inter-ocular bar but it may be absent.
Both species have both blue and green form females.
The only reliable way to distinguish is by close examination of the pronotum, the plate on top of the prothorax onto which the male fastens during copulation. Here are four comparative views of Azure and Variable female pronotums.