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Double gill mayfly (Arachnocolus)

Taxonomic group

Leptophlebiidae: Arachnocolus

Diagnostic features

Arachnocolus mayfly nymphs have double gills, long thin legs (particularly the femur and tibia), and a generally pale body colour.

Typical habitats

Arachnocolus larvae are most abundant in bush-covered, gravelly streams with cool and well aerated water.


Leptophlebiid mayflies feed by scraping diatom algae and other organic matter from stone surfaces.

Indicator value

  • Hard bottom: 8
  • Soft bottom: 8.1

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

Arachnolocus are not often found in high abundance, but they are indicative of good habitat and water quality, especially if other mayfly or stonefly groups are abundant. Arachnolocus has tolerance values of 8 (hard bottom sites) and 8.1 (soft bottom sites).