lurks beneath stones in cold water

Size
Length: 1–3 cm, Weight: 0.1–0.3 g
Lifespan
1–2 years
Diet
Larvae feed on algae detritus and small aquatic insects. Adults may feed on algae or not feed.
Habitat
Cold, clear, fast-flowing mountain streams and rivers. Hidden climbers of the rock face, lurking beneath stones in the coldest water.
Range
Found throughout the North and South Islands in cold, fast-flowing streams and rivers. Most common in alpine and hill country streams of the South Island and central North Island.
Endemism
Endemic
Main Threats
Water pollution from agricultural runoff and urban development. Sedimentation from land clearance. Climate change reducing water flow and increasing water temperatures. Loss of riparian vegetation.
Population
Stoneflies are widespread in New Zealand's alpine and hill country streams. Like mayflies, they are highly sensitive to pollution and warming water temperatures. Their presence indicates cold, well-oxygenated water.
Conservation Status
Not Threatened
Human Risk
harmless
Handling Note
native stonefly, indicator of clean water leave undisturbed
Conservation Note
Endemic insect; not assessed by NZTCS as invertebrates are generally outside the scope of current threat classifications.
Te Ao Māori
Stoneflies living in the remote headwaters were less visible to early Māori than lowland species but their presence in the cold streams would have been known to those travelling in the high country. They represent the purity of the mountain waters (wai māori) untouched by human activity. In modern conservation they are vital sentinels of climate change. As waters warm these cold-water specialists are among the first to retreat further uphill serving as a warning signal for the health of our alpine ecosystems.
It is not flashy. The introvert of the stream bed prefers to remain hidden. Unlike the flashy mayfly or the dramatic dobsonfly the stonefly nymph is flattened and cryptic perfectly camouflaged against the grey and brown stones of the riverbed. It clings tenaciously to the underside of rocks avoiding the full force of the current while grazing on detritus and algae. It is a creature of the shadows shunning the light and the surface. Adult stoneflies are equally understated. They are soft-bodied with long antennae and wings that lie flat over their backs like a folded cloak. They are weak fliers often scuttling along the ground or hiding in moss near the water's edge. Unlike mayflies they have a longer adult lifespan surviving for weeks to mate and lay eggs. Some species even lack wings entirely spending their whole lives crawling among the wet stones. Despite their shy nature they are tough survivors of the cold. They thrive in the icy meltwater of the Southern Alps where few other insects dare to tread. They are a critical food source for native fish like the koaro and bullies which have evolved specialised mouths to scrape them off rocks. To find a stonefly is to know you are in the headwaters where the water is cold the air is thin and the world is still wild. They are the quiet guardians of the high country asking only for cold water and clean stones. The stonefly's sensitivity to environmental change is both a weakness and a superpower. Their gills are exposed and delicate designed to extract oxygen from near-freezing water that holds more dissolved gas than warm streams can manage. When sediment clogs the gaps between river stones the stonefly suffocates. When farmers take water for irrigation the stream warms and the stonefly vanishes. But give them clean water again and they return within a season. They have no tolerance for compromise and that makes them the most honest witnesses a river can have. Where stoneflies live the water is good enough to drink.