Sympetrum striolatum (Common Darter)  

The common darters recorded in the Outer Hebrides are the usually melanic form which is typically found in extreme west and north of Europe, in Ireland, Scotland and Norway. This form was formerly classified as a separate species, the highland darter (Sympetrum nigescens) but the reliability of the characters have been questioned and it is treated in most publications as a form of common darter.
The latest DNA research indicates that it is not a separate species but just a dark morph of Sympetrum striolatum, the darker colouring benefiting survival in a colder, northern climate.
Although, it still appears as Sympetrum nigrescens (Lucas, 1912) on the Natural History Museum list of British species, the records on NBN are treated as S. striolatum.