The Ruddy Darter (Sympetrum sanguinem) is quite similar to the Common Darter (Sympetrum striolatum) and the Vagrant Darter.
However, the Ruddy Darter can be easily recognized by its completely black legs.
The other two Darters have yellow or brown stripes along the legs.
All three dragonflies have a black spot on top of their snouts, like a sort of mustache.
In the Vagrant Darter and Ruddy Darter, the black runs down the eyes' edges, turning the mustache into a drooping mustache.
The Common Darter is missing this and so it only has the black mustache on top.

1st & 2nd photo: Fochteloërveen Nature Reserve, Fochteloo, The Netherlands, 25 September 2014
3rd photo: Fochteloërveen Nature Reserve, Fochteloo, The Netherlands, 6 August 2016
4th photo: Naardermeer, The Netherlands, 22 August 2016
5th photo: Oostvaardersplassen, The Netherlands, 19 July 2021