Ephemerella notata (Eaton), 1887
The Yellow Evening Hawk
Nymphs: Nymphs with four pairs of plate like gills visible. Gills are held above the body and when viewed from above they do not extend beyond the sides of the body. Nymphs swim poorly with a characteristic 'S' shaped rocking motion.
Adults: Medium sized flies with three tails and large hindwings. The sub-imago of this species has pale yellowish grey wings with yellow venation. In the male the body is yellowish, with the last three segments pale amber in colour. In contrast, the female has an orange yellow body. In both sexes the legs are yellowish and the tails are yellowish with brown rings.
In the imago the wings are transparent with yellowish veins along the leading edges. The body is yellow olive and the underside has a distinctive pattern of lines and spots. The male has orange coloured eyes, while in the female they are greenish.
Separating from other species
Nymphs: The nymphs of Ephemerella notata have a distinctive rocking swimming style. The nymphs are light in colour and generally do not have any patterning on the body, apart from a series of dark marks on the underside of the body. They can be separated from the closely related Serratella ignita by the absence of any patterning on the legs and tails. Some workers suggest that the presence of distinctive marks on the underside of E. notata can be used to separate these species however this is unreliable as the marks are often present, albeit faintly, in S. ignita.
A definitive feature is the profile of the body. In S. ignita there are a pair of small spines on the upper surface of each body segments (a). These spines are absent in E. notata (b).
Adults: Ephemerella notata is superficially similar to Habrophlebia fusca however in E. notata there are small detached single veins at the edge of the forewings, between each of the major veins. H. fusca never has detached veins at the edges of the forewing.
Many workers use the presence of distinctive marks on the underside of E. notata to separate it from S. ignita, however this may prove unreliable as the marks are often present, albeit faintly, in S. ignita.
Habitat and ecology
Nymphs of this species live in rivers and streams either on in-stream vegetation or amongst the sand and gravel on the bed. They are usually found clinging to, or crawling amongst submerged plants and stones, although they may swim in short bursts if disturbed. The nymphs feed by collecting or gathering fine particulate organic detritus from the sediment.
There is one generation a year, which can overwinter either as eggs or as nymphs and emerges between May and June. Males of this species swarm at dusk and once mated, the female produces an egg mass which she holds under her tail. This egg mass is released as the insect flies above the water.
Ephemerella notata is less common than S. ignita, however its range has spread northwards considerably over the past 25 years.