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Siphlonurus alternatus (Northern summer mayfly)

There are few published records for Siphlonurus alternatus from mainland Britain, although it is known from several locations in Ireland.  Nymphs of this species typically live in deep pools in rivers and streams, but can also be found in calcareous lakes.  The large nymphs are good swimmers and typically swim in short, darting bursts.  They feed by gathering or collecting fine particulate organic detritus from the sediment.  There is one generation a year, which usually overwinters as eggs and emerges between May and August.

 


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Emergence of the adults typically takes place during daylight hours and males of this species can be found swarming at dawn and dusk.