Crowds thronging the streets in Golok, a pastoral region on the Tibetan plateau, signal the arrival of spring. Everyone is feverishly buying and selling. Groups of people huddle over trays of a strange-looking product. Men in black suits sit under big umbrellas with telephones glued to their ears, discussing something in hushed voices. A group of women squat on the ground, cleaning something with toothbrushes. A few steps away there is a cardboard box in the sun; a young woman guards its contents against curious onlookers. It seems as if everyone is carrying at least some of this curious product. People in restaurants pull it from their pockets and show what looks like a small, brown, dry caterpillar to their neighbours.

Wherever you go, people talk about one thing. Instead of exchanging the usual greetings, they inquire ‘do you have many yartsa?’ ‘What's the latest price?’, passengers on a bus say as a conversation starter. The words yartsa gumbu are on everyone's lips. Yartsa gumbu is the Tibetan name of a rather unusual organism, which looks like a larva with a horn growing from its head. It is a parasitic fungus (Ophiocordyceps sinensis) that feeds on caterpillars of certain species of moth that inhabit the Tibetan plateau. Advertised as a wonder drug, it commands high prices on the Chinese market and thousands of kilograms of yartsa gumbu are sold in China and abroad. But there is only one part of the world where it grows: this species of caterpillar fungus is endemic to the Tibetan plateau and the Himalayas.

Golok is one of the Tibetan regions that produce caterpillar fungus and where people have built their livelihoods upon it. During the several weeks a year when this fungus is dug from the ground, it becomes everyone’s primary concern. It captures the attention of people from all walks of life and often appears in unexpected contexts.

In Dawu, Golok's biggest town, in the house of a Buddhist monk, people wait for divinations. In gratitude for the monk's help, they offer him tea bricks, money, and caterpillar fungus. In a photo studio, a trader waits for his photographs to be developed.