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Ephemera danica (Green drake mayfly)

Ephemera danica is the most common of the British Ephemeridae.  It can be found in unpolluted rivers and lakes throughout the British Isles.  Nymphs of this species live in lakes and fast flowing rivers and streams with a sandy or gravely bed.  The nymphs dig into the gravel to form a tubular burrow and they use their gills to force the water through this burrow.  The nymphs feed by filtering or collecting fine particulate organic detritus from the water column.  Ephemera danica usually has a two year life cycle, however recent work has shown that in the warmer waters of Southern England it is able to complete its life cycle in one year.  The main flight period is towards the end of May, however adults are often present between April and November.

 


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Emergence of the adults takes place during daylight on the surface of the water or occasionally on a stick, stone or plant stem partially or entirely out of the water.. The males of this species can be found swarming throughout the day, and often swarming continues until dusk.

 

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 onto the surface at intervals, or by actually settling on the surface for short periods.  After several visits to the water the egg supply of up to 8300 eggs is finished and the spent female falls on to the surface.