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The Rhithrogena gratianopolitana is often confused with the March brown (=R.germanica) as their hatching period can overlap. This dun flies from March to May.
Males are easily distinguishable from female by the large eyes.
In the subimago (dun) the hind wings are characterized by a lighter colored border. In the male dun two black streaks are present on the compound eyes lowest edge, separated by a cream streak.
Ventral view.
This specimen was photographed during large hatches in the Piedmont alps. The hatch lasted several days. The duns were observed emerging during the warm hours of first spring days. The fish goes easily in activity with the critical mass of this insect on the surface.