Common Darter Dragonfly Sympetrum striolatum

Common Darter Dragonfly male
Common Darter Dragonfly female
The Common Darter Dragonfly, as its name indicates, is one of the most common dragonflies, not only in the UK but also throughout Eurasia.
The adult male (above left) has a reddish hue while the female (above right) is yellowy brown. Similar-looking subspecies include the Island Darter and the Highland Darter.
Common Darter Dragonfly
Common Darter Dragonfly
Common Darter Dragonfly
The "teneral" (recently-emerged) darter (above centre) is light yellow with lemon/lime yellow "pterostigma" (the stained glass plane at the top outside edge of the wing). Females darken (above right) progressively browner with age, occasionally with a red tinge, and males redden, but less red than the Ruddy Darter, which has a clubbed end of abdomen ("tail").
Common Darter Dragonfly Reddish male
Common Darter Dragonfly The male's pterostigma reddens and there may be a reddish vein
Common Darter Dragonfly A mating pair
Common Darter Dragonfly
Common Darter Dragonfly
Common Darter Dragonfly
A diagnostic feature, if close enough, is said to be the yellow stripe on the black leg, although the Red-veined Darter also has these.