You will also see the scientific name of this genus written as Rithrogena rather than Rhithrogena, particularly in older books on angling entomology, but I have also seen Rithrogena used in scholarly research articles. The correct spelling is Rhithrogena.
The Olive Upright, a close relative of the March Brown, is found on just about every river in Britain, and it is probably the most abundant spring fly of all. The nymphs are flattened stone clingers with small gills each comprising a plate plus a tuft of fine filaments. Unlike the March Brown, the Olive Upright and are found in all kinds of running water, including chalkstreams and acidic spate rivers.
The dun hatches throughout the day from May until July. Hatches are often heaviest towards evening, and at that time the spinners also appear, but their egg laying occurs very late in the day, so that the duns are usually far more important as far as trout fishers are concerned.
This is a particularly important river fly in spring, and it is also well worth imitating if you are fishing for wild brown trout at that time of the year. The hatches are less dense than those of the other common Rhithrogena species in Britain, the March Brown, Rhithrogena germanica, but in compensation you are likely to have a much longer fishing day with Olive Uprights on the water and, of course, they are about for two or three times as many days as is the case with the March Brown.
Having fished on more than 200 rivers in Britain and Ireland, I have yet to find one where Olive Uprights are not present.
Male and female duns are very similar in appearance. Although the nymphs have three tails, as adult flies the Olive Upright has just two tails.
Female Olive Uprights are slightly larger on average than the males, but as if to make up for it the males have much larger eyes than their mates. Body colouring is very similar in both sexes: greyish brown, but the male's body is more boldly ringed with orange bands. Depending on how the light catches them, the forewings of the duns are dark to mid blue-grey, while the largish hindwings are more buff than grey.
Because the duns trickle hatch over several hours each day, it is easy to underestimate how abundant these flies are, especially on northern and western rivers. (They are reported to be less in evidence on the very slow-flowing rivers of southeast England.)
It is not until evening, when the male spinners begin swarming, that you are likely to become aware just how many of these flies hatch in a single day. I have seen swarms of several hundred male Olive Upright spinners dancing in the late afternoon sunlight beside a small stony stream. Once the cool of evening descends they seem to melt away; however, if you watch a swarm you will see plenty of females dropping in a selecting a mate. Paired, they then leave the swarm, and that is probably the last you will ever see of the male, although the female will eventually return to the river to deposit her eggs, either by sitting on a semi-submerged stone or by flying low over the water and dipping her ovipositor into the surface to release eggs periodically. Females fly slowly upstream, depositing eggs until their mission is competed; then they die either on the water or nearby. Needless to say, it is the dead females lying on the surface that trout find easiest to seize, and so rises to spent Olive Uprights are unhurried.
The body colour of Olive Upright spinners (males and females alike) is light to mid brown and the wings are brilliantly translucent, clear except for a bronze flush that is progressively darker near to the wing bases, and patterned with beautiful light-brown veining.
Such a common and widespread river fly deserves a close imitation rather than a general representation multi-purpose 'olive' such as Greenwell's Glory, for example. In Matching the Hatch, fishing tactics for the Olive Upright season are discussed in some detail on pages 70 to 73, where I give tying details for Guy Mawle's superb Olive Upright pattern.
If you are limited to shop-bought flies, I suggest a size 12 Greenwell's Glory for the dun stage, while for the spinner fall switch to a Tups Indispensable of the same size. They work reasonably well in fast water, but in more gentle glides a closer match is likely to give better results, especially on hard-fished river beats.
Etymological note: We use the terms flyfishing and flyfisher throughout our pages, but some people still write fly fishing, fly fisher and fly-fishing techniques.
Entomological note: The diversity and particularly the abundance of flylife (or if you prefer fly life) on rivers and streams in Britain and Ireland has declined dramatically over the past forty years. We support the Riverfly Partnership's campaign to raise awareness of this issue, to involve anglers and others in scientific monitoring of water quality via aquatic invertebrate diversity, and to promote actions to halt and reverse this decline.
In identifying up-winged flies to species level we make extensive use of two Freshwater Biological Association publications:
A key to the Adults of the British Ephemeroptera with notes on their ecology; J M Elliott and U M Humpesch (1983). FBA Scientific Publication No. 47.
Larvae of British Ephemeroptera: a key withy ecological notes; J M Elliott, U H Humpesch and T T Macan (1988). FBA Scientific Publication No. 49.
For flyfishers on stillwater, river and stream there is an illustrated guidebook with advice on corresponding artificial flies plus fishing tips:
Matching the Hatch, Pat O'Reilly; Quiller Publications (1997, latest reprint 2010) ISBN 978 1 85310 822 8