By Nigel Binks, DOC Freshwater Technical Advisor
High in the windswept mountain tops of the West Coast, where tarns sit like mirrors among sphagnum mosses and alpine herb fields, a Department of Conservation expedition has uncovered a remarkable surprise – an endangered caddisfly discovered hundreds of kilometres from where it was originally discovered.
Searching remote ecosystem
The goal of the expedition: To survey lowland streams and remote alpine seeps, springs, and tarns for some of New Zealand’s most threatened freshwater invertebrates.
I set out on the expedition with a research party of seven, including Earth Sciences caddisfly expert Brian Smith, freshwater specialist Steve Pohe, Canterbury Museum Research Fellow Tim Hitchings, volunteers and DOC staff.
These isolated, mountain‑origin habitats are among the country’s most remote ecosystems. Perched high on rugged plateaus, they are small, cold, and exposed, yet home to species found nowhere else on earth.
Bound by silk, armoured in mineral fragments and crystals
While surveying one of the tarns, Brian noticed the tiny protective cases of a predatory species of caddisfly larvae among the sediments.
Many caddisflies build intricate portable homes from sand, plant fragments, or tiny stones, bound with silk. The caddisfly larvae they’d found roam in fine sediments, feeding on the larvae of other invertebrate species, worms, and mayfly nymphs, using two pairs of spine‑covered raptorial limbs, perfectly adapted for capturing prey.
Their silk acts as an underwater glue, allowing larvae to construct an incredible range of protective cases and nets which many caddisflies are known for. In fact, the way different lineages use silk is one of the characteristics of the caddisfly suborders, which is why caddisflies are often referred to as the “underwater architects” of our freshwater ecosystems.
Flecks of tiny mica glittered in the sunlight, bound within the larvae cases. Several larvae were collected for identification. Under the microscope, we observed an extraordinary collection of shiny mineral flakes bound together amongst the tiny stones that formed the larval cases – flecks of silica mineral dust and small clear grains of quartz had been naturally incorporated into the insects’ armoured home.
A rare caddisfly found hundreds of kilometres from their originally known range
More importantly, this species of caddisfly was classified as Declining, originally identified from Kokiri where their original habitat has been destroyed, and from other locations in the greater Nelson area. Its discovery in a remote alpine tarn, hundreds of kilometres away from Kokiri, dramatically expands the understanding of its range and provides a new hope for its survival beyond their origin habitat.
For freshwater scientists, this find highlights how much remains hidden in New Zealand’s landscape, and how the true distribution of many species remains poorly known or at risk of disappearing before they are properly understood.
Targeted surveys of remote, under‑sampled habitats provide the essential data needed to correctly assess species under the New Zealand Threat Classification System (NZTCS). Each new locality record helps refine threat rankings, guide conservation priorities, and distinguish truly rare species from those simply under‑surveyed.
More than a curiosity of nature
Freshwater invertebrates underpin healthy rivers and wetlands, cycling nutrients and providing food for fish, birds, and other wildlife. These tiny caddisfly larvae are part of a delicate food-web shaped over millions of years – proof that even in the most remote corners of the country, nature still holds surprises waiting to be discovered.
