Invertebrates
Alderfly
Sialidae · also called alderflies
Breathing through feathery gills along its body, an alderfly larva hunts other small invertebrates in a clean, fast-flowing stream, a life it will leave behind entirely once it crawls onto land to pupate in the damp soil of the riverbank.
Overview
The alderfly, family Sialidae, is native to streams, ponds, and wetlands across much of the world. Its gilled aquatic larva, unusual land-based pupation, and role as a simple indicator of clean water make it a small but ecologically meaningful insect found across temperate freshwater habitats.
A life split between two very different worlds
The alderfly’s larva spends its entire early life breathing underwater through delicate gills, only to abandon the stream completely and crawl onto land to complete its transformation in damp soil, a brief return to water-dependence followed by a short, almost dry-land final chapter as a weak-flying adult.
Status
Not Evaluated for conservation status, found across suitable clean streams, ponds, and wetlands throughout much of the world.
Alderfly: common questions
How long does an adult alderfly live?
Only a few days; adults barely feed and spend their brief lives focused almost entirely on finding a mate before dying.
Why are alderfly larvae considered a sign of clean water?
The larva cannot tolerate pollution and survives only in clean, well-oxygenated streams and ponds, so biologists use its presence as a simple indicator of good water quality.
Is the alderfly related to the dobsonfly?
Yes, both belong to the same insect order, though the alderfly is considerably smaller and less dramatic in appearance than the large-jawed dobsonfly.
Where are alderflies found?
In streams, ponds, and wetlands across much of the world, with the greatest diversity in temperate regions.