Alainites muticus (Linnaeus, 1758)

the Iron Blue

Nymphs: Streamlined nymphs with plate-like gills, with the first pair much smaller than the others.

Adults: Small flies with two tails and small oval hindwings.  The sub-imago has dull grey blue wings and a dark brown body that is sometimes tinged with olive.  The legs are pale to dark olive brown, whilst the tails are dark grey.  The imago has transparent wings and pale grey legs and tails.  The body in the female is dark claret brown, whilst in the male it is translucent white, with the last three segments being dark orange brown.

Nymphs: Alainites muticus has distinctive narrow-bodied nymphs that do not have a distinct black band across the tails.  There are seven pairs of gills, although the first pair is very small and easily overlooked in mature nymphs.

Adults: Alainites muticus can be distinguished from other adult Baetidae by the presence of three veins on the oval shaped hind wing, the second of which is forked.  The third vein, which runs along the lower edge of the wing, is missing in Nigrobaetis digitatus and N. niger.  It is often difficult to see the third vein, and care must be taken to double check whether it is present or not.

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. 

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 surfaces.

Alainites muticus is a widespread and common species that is found throughout the British Isles.  It is relatively uncommon in the South-east of England.