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Baetis vernus (Medium olive)

Baetis vernus is common in England and Wales but has a highly localised distribution in Scotland and Ireland.  Nymphs of this species live chiefly in the pools and margins of rivers and streams, where they live amongst the sand and gravel of the bed or on in-stream vegetation.  The nymphs swim in short, darting bursts amongst the substrate, or climb amongst the vegetation.  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 a year, one with overwintering eggs that emerge in the spring and another that grows over the summer and emerges later in the year.  In some years there may be further generations however adults are generally only seen between April and October.

 


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Emergence of the adults takes place at the surface of the water during the day and at dusk.  The males of this species swarm throughout the day but typically stop before 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 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.