The UK is home to two Demoiselle (Calopteryx) species.
At maturity, the males, having darkly coloured wings, are quite distinct from females but immature males of one, the Beautiful Demoiselle (C. virgo), have brown-tinted wings which could be confused with females. The females of the two species can be very tricky to separate.
So, first, do we have a male or a female?
Demoiselle (Calopteryx) female
Demoiselle (Calopteryx) male