Large Dark Olive Mayfly - Baetis rhodani


This family is characterised by two tails and tiny oval shaped hindwings. The pairs of short veins between each of the long veins in the forewing indicate that this is a Baetis species. B. rhodani is the largest sized member of this group, especially the early hatch, later in the year specimens become smaller. It is also one of the earlier mayflies to hatch out.

Baetis larvae can be distinguished from other mayflies by the fact that the middle filament of the "tail" is shorter than the outer two.  B. rhodani larvae have small spines in addition to cilia along the edge the gills (400x magnification needed); if these are absent the larva is it is one of the four other Baetis species. 

Identification difficulty

Usually around moving water.

When to see it

All year round, but especially from March until autumn.

Life History

Once mated the female finds a partially submerged stone and folds her wings back over her body. She then crawls through the water surface and lays her eggs directly onto the submerged stone. She lays around 4500 eggs individually side by side so that they form a discrete patch of eggs on the stone. The larvae generally live amongst the sand and gravel on the bed of moving water. They feed by scraping algae from submerged stones, etc. or by collecting fine organic materials from the bed.

UK Status

Frequent and widespread in Britain

VC55 Status

Common in Leicestershire and Rutland.

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Leicestershire & Rutland Map


Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015

UK Map