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R. semicolorata is an is in Europe widely spread and its hatches are important for the fly angler.
During May and June I often come across hatches and its spinner fall at dusk has often gave nice trouts on spent imitations.
It is a medium size mayfly with a body of 10-12 mm.
In spite of the english name (yellow upright) its habitus as spinner is more rusty orange to me.
Genitalia detail, ventral view: R.semicolora typical penis lobus