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Swimming mayfly (Rallidens)

Taxonomic group

Rallidentidae: Rallidens

Diagnostic features

Rallidens mayfly nymphs have a torpedo-like body form, fringed caudal filaments (“tails”), short antennae and double abdominal gills (the inner gill being fringed).


Typical habitats

They are most common in stony or gravelly, bush covered streams


Rallidens larvae may feed on biofilm (algae and other microorganisms) and plant detritus on the streambed.

Indicator value

  • Hard bottom: 9
  • Soft bottom: 3.9

The tolerance values (ranging from 0 to 10) give an indication of which are the sensitive taxa (values of 8 or more) and which are the tolerant taxa (values of 3 or less). For more information see: Indicator species

Abundances of Rallidens suggest good habitat and water quality conditions, especially if other mayfly or stonefly groups are abundant. They have tolerance values of 9 (hard bottom sites) and 3.9 (soft bottom sites).