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Fringe gilled mayfly (Isothraulus)

Taxonomic group

Leptophlebiidae: Isothraulus

Diagnostic features

Isothraulus mayfly nymphs have a flattened body form, and the double gills are extensively fringed.

Typical habitats

Isothraulus larvae are rarely found in high abundance, but they are most common in small, slow-flowing bush covered streams in the north of the North Island.


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

Indicator value

  • Hard bottom: 8
  • Soft bottom: 7.1

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

The presence of Isothraulus suggests good habitat and water quality conditions, especially if other mayfly or stonefly groups are abundant. They have tolerance values of 8 (hard bottom sites) and 7.1 (soft bottom sites).