haunts the clean stream margins at dusk
- Size
- Length: 1.5–3 cm
- Lifespan
- 1–2 years
- Diet
- Larvae are aquatic predators feeding on small insects and mayfly nymphs. Adults do not feed or may take only water and nectar.
- Habitat
- Near margins of clean, slow-moving streams and lakes. The twilight residents of the New Zealand freshwater world.
- Range
- Throughout North and South Islands in lowland streams and lakes with clean, well-oxygenated water. Most common in areas with native forest cover and stable stream banks.
- Endemism
- Endemic
- Main Threats
- Habitat degradation from agricultural runoff, stream sedimentation, removal of riparian vegetation and water pollution. Sensitive to low oxygen levels.
- Population
- A primitive and ancient group of insects. Their presence is a classic indicator of high water quality and a healthy riparian environment.
- Conservation Status
- Not Threatened
- Human Risk
- harmless
- Handling Note
- native alderfly larva, aquatic predator leave undisturbed
- Conservation Note
- Endemic insect; not assessed by NZTCS as invertebrates are generally outside the scope of current threat classifications.
- Te Ao Māori
- Alderflies represent the principle of The Quiet Margin. They serve as a symbol of the connection between land and water. Known as the silt-dwellers, they occupy a niche as a reminder that the most ancient lineages are often the most unassuming. They remind us to respect the living water and the hidden residents of the mud.
Wings fold like a tent. The alderfly is the ancient aviator of the New Zealand riverbank. It folds smoky dark wings in a steep tent-like shape over a robust heavy body. This insect represents a lineage that has remained largely unchanged for millions of years. As adults, they are short-lived and non-feeding. They focus entirely on finding a mate and returning eggs to the water's edge.
The larvae are the underwater tigers of the benthos. They live buried in silt and mud of slow-moving streams. These benthic hunters are formidable predators. They are equipped with powerful forward-facing jaws used to ambush other small invertebrates. To survive in the low-oxygen environment of the streambed, they possess delicate feathery gills. These are arranged in pairs along their abdomen. They allow the larva to extract oxygen directly from the water.
This life cycle is a definitive sign of living water. Alderflies require stable, unpolluted sediment and a complex food web to reach maturity. They represent the connection between land and water. They illustrate how the health of our terrestrial forests is linked to the predatory life hidden beneath the surface of the mud.
While currently not threatened, alderflies are sensitive indicators of sedimentation and loss of riparian vegetation. To encounter an alderfly resting on a riverside fern is to witness a survivor. It has mastered the art of freshwater continuity.
It does not ask for much. Just clean water and stable banks. And it takes both.