Without it, the dung persists. The paddock fills with old scats. The grass grows through them. The nutrients remain locked inside. The NZ Nail Fungus solves this. It grows on horse dung. Old dung. Dung that has sat for weeks. The fruiting bodies look like nails. Black. Pointed. A flattened head on a thin stem. The head is the spore-bearing surface. The stem anchors the dung. The nails stand upright. Two centimetres tall. Sometimes shorter. They grow in groups. Ten on a single dropping. Fifty. The dung blackens. It shrinks. Within months, it is gone. The fungus has consumed it. The nutrients return to the soil. The cycle continues. Threats are straightforward. Fewer horses. Horse numbers in New Zealand peaked in the 1970s. Two hundred thousand. Now one hundred thousand. The fungus needs horse dung. It will grow on cattle dung but poorly. Smaller fruiting bodies. Fewer spores. The fungus evolved with horses. Horses evolved in North America. The fungus arrived in New Zealand with horses. European settlers brought both. The first shipment of horses landed in 1814. The fungus arrived in their guts. In their dung. It spread across the country. It became common. Now the horses are fewer. The paddocks are empty. The fungus retreats. Diet is coprophilous. Poronia erici decomposes the lignified plant fibre in herbivore dung. Horses digest poorly. Their dung contains grass stems, husks, seeds. The fungus breaks down the lignin. It leaves behind a dark, crumbly residue. The residue becomes soil. The process takes three to six months. The fungus fruits at the end. The nails appear. They release spores. The spores land on fresh dung. The cycle repeats. Without fresh dung, the fungus dies. No dormancy. No soil phase. Only dung. Only horse dung. Range across New Zealand follows horse distribution. Highest densities in Waikato, Canterbury, and Otago. Horse studs. Trekking centres. Rural properties. The fungus also occurs in the North Island near Auckland, Manawatu, Wairarapa, Hawke's Bay, Taranaki. South Island populations in Nelson, Marlborough, West Coast, Southland. Absent from areas without horses. Stewart Island has no horses. The fungus does not occur there. The Chatham Islands have horses but no records. The fungus may be present. No one has looked. Habitat is pastoral. Improved pasture. Grazed paddocks. Stock yards. Racecourses. The dung must be exposed. Not buried. Not scattered. The fungus needs dung in the open. Sunlight. Rain. Air movement. Dung in forest does not host it. Too dark. Too damp. Dung in stables does not host it. Too dry. The fungus needs the middle ground. Paddocks with horses. Dung dropped in autumn. The nails appear in winter. By spring, the dung is gone. The paddock is clean. The horses return. The cycle continues or stops. The horses are fewer. The fungus declines.