British distribution: Widespread and locally common in most of England and Wales, but much rarer in northern England. In Scotland largely restricted to the west coast, and possibly a separate species or subspecies (see below). Also an immigrant from the continent, resulting in scattered records outside its breeding range.
Sympetrum striolatum is a true dragonfly (i.e. a member of the suborder Anisoptera, rather than the suborder Zygoptera, the damselflies). It is generally the commonest of the 'darter' dragonflies in Britain. Hammond (1985) gives the wingspan as 58 mm and the average overall length as 37 mm., making it a conspicuous insect, though not as large as the hawker dragonflies.
Identification and variation
In west Scotland, individuals have more black along the sides of the thorax and abdomen and more black on the legs. They have been regarded as a separate species, S. nigrescens, the Highland or Black-legged Darter, or as a subspecies, but intergrade with more typical S. striolatum where this occurs. They are probably best regarded as a melanic form of S. striolatum (thermal melanism?).
There are several other British Sympetrum species and identification requires reference to a well illustrated guide such as Hammond (op. cit.), Brooks & Lewington (2002) or Dijkstra & Lewington (2006). Perhaps most similar amongst native species is S. sanguineum, a much more local dragonfly of southern and eastern England. In this species the male has a noticably narrowed upper abdomen. Very similar indeed to S. striolatum and distinguishable only by face-patterning and genital characters (see Longfield, 1949, Dijkstra & Lewington, op. cit.) is S. vulgatum, a rare vagrant from Europe.
As with other dragonflies, the larval (nymph) stage is aquatic, a predator in still or slow-flowing waters.
Remarks on dragonflies in biodiversity assessments are given in the account of Cordulegaster boltonii.