Red-veined vs Common vs Ruddy

Unless you are fortunate enough to come across a site in early autumn where breeding took place in May/June then you are most likely to encounter mature male Red-veined Darters flying well out over (shallow) water. In colouration they are more like Ruddy Darter but they have a pale stripe on the side of the thorax (Ruddy is plain, Common has a red panel) which can be picked out at some distance. The wing-veins are very red and conspicuous. If you are fortunate enough to be able to approach them more closely (or they rest out on vegetation on the water) the other features become obvious.

The key features to distinguish the three darters are in the table below (m means mature male, f female, im immature male, if immature female)

The only comparison image I'll put up is one showing the wing detail of Red-veined Darter and male Common Darter (click to bring up larger in a new window)