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Baetis muticus (Northern Iron Blue Mayfly)

Baetis muticus is a widespread and common species that is found throughout the British Isles.  It is relatively uncommon in the South-east of England.  Nymphs of this species live chiefly in riffle sections of rivers and streams, where they live in gravel, sand or mud on the bed of the watercourse.  The nymphs are good swimmers and typically swim in short, darting bursts.  They feed by scraping algae from submerged stones and other structures, or by gathering or collecting fine particulate organic detritus from the sediment. 

 

There are two generations per year - a slow growing winter generation and a much faster summer generation.  This results in a fairly long flight period, with adults being present between April and October. 

 


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Emergence of the adults typically takes place on the surface of the water during daylight hours.  The males of this species can be found swarming throughout the day, however swarming stops at the onset of dusk.

 

Once mated, the female flies to the river and lands on a partly submerged stone.  She then folds her wings and pulls herself under the water to find a suitable place to lay her 3500 eggs.  The eggs are laid individually alongside each other to form a contiguous patch of eggs.  Once completed, she will sometimes climb back out of the water and fly away, however more often than not, she will be swept away by the current.  In some cases the female will fly to the river, where she descends to the surface of the water and releases her eggs in several batches by dipping the tip of her abdomen into the water surface.