The Olive Upright (Rhithrogena Semiclorata)
A very important food source for both trout and grayling on the Rivers Usk and Wye
This insect is a very important food source for the River Usk and Wye as it arrives at the end of the Grannom and March Brown hatches and the Dark Olives have diminished in numbers. They are only normally found in this South Eastern area of Wales, which is lucky for us.
They start to hatch from dawn till dusk from April through to August/September. The nymphs are stone clingers and are to be found in riffled water and they feed upon algea on the rocks and stones of the river. The nymph has three tails and can appear quite translucent but with an olive tinge. The wing cases are seen to be a lot darker as it nears time to emerge from the water into the adult dun which incidentally only has two tails.
The males will bunch together ready to mate but the females will then return to the river as spinners and will deposit their eggs by dipping there tails onto the water surface.
Female Spinner from another angle
Dave Collins Ducks Dun is a great pattern to imitate this fly. When the trout are on them they seldom will look at anything else.
Follow this link for the associated article http://www.gwentanglingsociety.co.uk/articles/fishing-skills/duck-s-dun-patterns-a-generic-tying-style-well-worth-exploring.