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Baetis scambus (Small dark olive)

 Nymphs of this Baetis scambus typically live in the riffle areas of rivers and streams either on in-stream vegetation or amongst the sand and gravel on the bed.  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.  This results in a long flight period with adults present between February and November.

 


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Emergence of the adults probably takes place at the surface of the water during daylight hours.  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 around 1200 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.

 

Due to the problems with the identification of nymphs, it is difficult to compile a complete distribution for this species.  Baetis scambus is however, thought to be the more common than Baetis fuscatus.