From Eat the Buddha: Life and Death in a Tibetan Town, by Barbara Demick (Random House, 2020), Kindle pp. 100-101:
Tibetans also discovered a niche that was almost uniquely their own: collecting medicinal herbs. Herbs were commonly used in both Chinese and Tibetan medicine, and many of the more valuable were found on the Tibetan plateau. Beimu, an alpine lily used to treat coughs, grew at altitudes of more than 10,000 feet, and Tibetan nomads were perfectly situated to collect it.
Most lucrative was Cordyceps sinensis, a prized ingredient in traditional medicine, believed to boost immunity, stamina, and lung and kidney function. Tibetans call it yartsa gunbu, meaning “summer grass, winter worm,” or simply bu, “worm,” for short. [In Chinese, it’s 冬虫夏草 dōng chóng xià cao ‘winter worm, summer grass’.] The worm is actually a fungus that feeds on the larvae of caterpillars. In the past, the worm was commonplace enough that Tibetans would feed it to a sluggish horse or yak, but the Chinese developed a hankering for it that sent prices soaring. Chinese coaches with gold-medal ambitions would feed it to athletes; aging businessmen would eat it to enhance their sexual potency. At one point, the best-quality caterpillar fungus was worth nearly the price of gold, as much as $900 an ounce.
Tibetans had a natural monopoly on the caterpillar fungus. Non-Tibetans didn’t have the local knowledge or the lung capacity to compete. The best worm was in Golok, northwest of Ngaba. Nomadic families would bring their children with them, sometimes taking them out of school because their sharp eyesight and short stature allowed them to more easily scan the ground for the worm amid the grasses and weeds. The season ran for approximately forty days of early spring, the time when the melting snow turned the still-brown hills into a spongy carpet. The families would camp out for weeks in the mountains. In a good season, a Tibetan family could make more in this period than a Chinese factory worker could earn in a year.
The Communist Party would later brag about how their policies had boosted the Tibetan economy, but the truth was that nothing contributed as much as the caterpillar fungus, which according to one scholar accounted for as much as 40 percent of Tibetans’ cash earnings. Unlike earnings from mining and forestry, industries that came to be dominated by Chinese companies, this was cash that went directly into the pockets of Tibetans. The nomads acquired the spending power to support the new shops and cafés. The golden worm was part of a cycle of rising prosperity.
Until the 1980s, trade between the Tibetan plateau and southern China had gone only in one direction. Tibetans were eager customers for the newfangled electronics and ready-to-wear clothing stamped out by China’s new factories, but Han Chinese didn’t have much taste for Tibetan products like dairy and lamb. The medicinal herbs gave the itinerant traders something to put in their suitcases when they went on shopping trips to Shenzhen and other southern Chinese cities.