Sometimes old names for flies are more evocative than their modern monikers. That’s certainly the case for the Small spurwing (Centroptilum luteolum). Its current name is derived from the adult having a small spurshaped hind-wing, but it was once called the Pale watery, Little sky blue dun or Little amber spinner. The Small spurwing is widespread and common, found throughout the British Isles. It has a more localised distribution in Scotland, where it is more often encountered in standing rather than running water. Nymphs swim in short, darting bursts among the sandy substrate, or climb water crowfoot and other water weeds. Once mature (body: 6-8mm, wing: 5-7mm) they emerge from the surface throughout the day before flying to bankside vegetation and transposing to a spinner. In summer they often delay emergence to avoid warmer temperatures. Irish entomologist John Harris described the wings of the dun as being “of the same peculiar shade of very pale blue as the feathers on the upper surfaces of the wings of terns and some sea gulls”, and in the correct light you can see what he means. The body of the spinner is a beautiful russet on the upper side, and a very pale yellow below. Males swarm just above the surface in the afternoon and often into twilight. After mating the females return to the river where they dip the end of their body into the water and release up to 2,500 eggs, before falling spent on the surface. There are usually two generations a year: one overwinters as nymphs and emerges in spring; and a fastgrowing summer generation. This results in a long flight period, the adults present April to November.
Did you know?
Frederic Halford described three species, including Centroptilum luteolum as Pale wateries, however the name is now more normally used to describe Baetis fuscatus.