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The H.sulphurea hatches from May to August. The female imago, afer laying the eggs by flying and rythmically dipping the abdomen in the water, fall as spent in the stream.
The color is bold bright, almost phosphorescent yellow
At first glance and from the distance it may be confused with the real Mayfly (E.Danica), but the E.sulphurea is smaller and has two cerci.
ventral view