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Rhithrogena semicolorata (Olive upright)

Nymphs of Rhithrogena semicolorata live chiefly in the riffle sections of rivers, where they feed either by scraping periphyton from the substrate or by gathering fine particulate organic detritus from the sediment.  The nymphs are usually found clinging to submerged plants and stones, although they may swim if disturbed. 

 

There is one generation per year that overwinters as nymphs.  As growth rates vary with water temperature, the period over which adults emerge is variable, but adults have been found between April and September in the British Isles.

 


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Emergence of the adults typically takes place from dawn until dusk at the surface of the water.  Males can be found swarming throughout the day but rarely into the evening.  Once mated, the female flies upstream and descends to the surface of the water to release a few eggs by dipping the tip of her abdomen on to the water surface at intervals, or by actually settling on the surface for short periods.  After several visits to the water the egg supply is finished and the spent female falls on to the surface.