Stoneflies are not beautiful like butterflies or dramatic like dragonflies. They are drab – brown, greenish, grey – with long antennae and two pairs of wings that fold flat over their bodies. They do not bite or sting. They do not eat crops. They simply live in clean, cold streams, eating algae and dead leaves, being eaten by fish, and serving as the most honest water quality test you will ever find. When stoneflies disappear, the stream is already dead. Size and sensitivity made the giant stonefly special. A 5-centimetre nymph is a hefty creature – thick-bodied, heavily armoured, with sprawling legs and a pair of tails longer than its body. It crawled across the streambed, grazing on algae and detritus, hiding from eels and trout. It breathed through gills located at the base of its legs – a delicate system that required high oxygen levels. Stoneflies cannot survive in warm, stagnant, or polluted water. They need cold. They need clean. They need oxygen. The adult giant stonefly was even more spectacular. It emerged at night – usually in late summer – crawling onto a rock or a tree trunk, splitting its nymphal skin, and pulling out its folded wings. The wings inflated, hardened, and turned translucent, veined like stained glass. The adult lived for only a few weeks – long enough to mate, lay eggs, and die. It did not eat. It had no mouthparts. Its entire adult existence was a single, desperate reproductive sprint. It anchored the food web. Stonefly nymphs are a major food source for native fish – eels, bullies, galaxiids. They break down leaf litter, turning coarse organic matter into fine particles that smaller creatures can eat. They are the middle managers of the stream ecosystem – unglamorous, essential, invisible until they are gone. Deforestation, agriculture, and irrigation destroyed it. When Europeans cleared native forest for pasture, the soil ran off the hills and into the streams. Stonefly nymphs cannot breathe in silt. Their gills clog. Their movements slow. They suffocate. At the same time, irrigation lowered water levels and raised water temperatures. Stoneflies need cold water. Warm water holds less oxygen. They suffocate again. Farm runoff – cow manure, fertiliser, pesticides – poisoned the water. Stoneflies are exquisitely sensitive to pollution. They are the first to die and the last to return. The giant stonefly, being larger and needing more oxygen than its smaller cousins, was the first to go. By the 1930s, it was gone. The streams still flowed, but the sentinel was absent. No one noticed at the time. Stoneflies are easy to overlook. That is the point. That is also the tragedy. The river sentinel is a name for something you will never see. A summer night, a gravelly riffle, and a winged insect the size of your palm, emerging from the water like a ghost. It used to happen here. It does not happen now.