From early May to mid-June, villages and schools on the Tibetan plateau stand empty, building projects languish for lack of workers, and in many districts only the very young, the aged, and the infirm are to be found at home. Everyone else has scrambled to the highlands to dig yartsa gunbu, or Caterpillar Fungus, a magical creature that is half-plant, half-worm.

No development expert could have crafted a more perfect export product than the mysterious and exotic yartsa gunbu,in which Tibetans enjoy a natural and seemingly industructable monopoly. It grows thinly scattered and only on the high plateau; it requires a lot of labor but only very simple equipment to collect; it cannot be cultivated, and it seems invulnerable to overharvesting – at least, so far.

The Tibetan name yartsa gunbu means “summer herb winter worm.” The Chinese name is chongcao, meaning “insect grass.” It is called Cordyceps Sinensis in Latin. What is it? Wikipedia explains: “Caterpillar fungi are the result of a parasitic relationship between the [cordyceps] fungus and the larva of the ghost moth…. The fungus germinates in living organisms … and then the cordyceps grows from the body of the insect.”

In other words, what you have worthy of a horror film — at least from the point of view of the poor caterpillar. The fungus invades the caterpillar, filling its entire body as it grows, killing the caterpillar and mummifying it. The fungus then grows out of the head of the caterpillar, continuing to grow until the fungus protrudes from the soil surface, a small brown finger reaching skyward. It releases its spores into the air and then it withers, still attached to the caterpillar, the two conjoined as if they are one creature: half plant, half worm.

Caterpillar fungus takes great skill to find, for the fungus protrudes only one or two inches from the ground and takes keen eyes to discern among the vegetation. The best pickers are usually children aged 8-15. A good picker can harvest more than fifty worms a day. Much folklore has sprung up to aid in worm-finding. One story is that the bent tail of one fungus points to the next, allowing the picker to move from worm to worm.

Thanks to yartsa gunbu, the Tibetan plateau has enjoyed an unprecedented economic boom, especially in the last ten years as demand has soared. In Kham the results are evident in the many new homes being built and motorcycles that have replaced horses as transportation of choice. Because of its obvious importance to the Tibetan economy, this past May a Kham Aid team undertook an unofficial investigation into the yartsa gunbu market.

We learned that Yartsa gunbu consumers are to be found in virtually every country of the world but by far the biggest markets are China and Japan where the worm is thought to be potent medicine. One website claims that caterpillar fungus is “the longevity and energy mushroom used by the Chinese nobility for more than 3,000 years,” and that it can treat “cough, anemia, tuberculosis, lower back pain,… impotence, infertility, irregular menstruation, night sweats, and senile weakness.” Similar claims are made by other sellers.

Generally speaking, Tibetan pickers sell the worms to middlemen who come to population centers like Kangding and Yushu in search of product. During the yartsa gunbu season, impromptu outdoor worm markets appear on city streets and bustle with activity as buyers and sellers haggle for the best prices. Sellers can also be found by the roadside waving bags of worms at passing traffic. Buyers transport the worms to major cities where the worms are cleaned, packaged, and distributed to retailers for sale.

Naturally, the closer you get to the source, the lower the price (the price also varies with the size and condition of the animal). We did not look at the rural market, which varies widely from place to place, but we did ask around in towns, using local proxies to avoid the inflated price that outsiders inevitably must pay. In late May this year the Kangding market price averaged about $2.50/worm and the price in Sershul, in the far northwest of Sichuan near the Qinghai border, was roughly $2/worm.

Compare these figures to retail prices in a place like Monterey Park, California where there is a large prosperous Chinese community and a healthy demand for traditional medicines. In Monterey Park the worms go for about $60 each—thirty times higher than the price in Sershul. Of course your mileage may vary depending on season, packaging, worm quality, and your bargaining prowess. The $58 of profit per worm is shared among middlemen – usually several of them – who inhabit each stage of worm trade. China Tibet Information Center estimates that the total market in China is worth 2 billion yuan (US$300,000) a year.

Because yartsa gunbu is extremely lucrative to the pickers, worm-hunting territory is zealously guarded during collecting season by the community to which it belongs. With the stakes so high, fights over worm turf can easily turn violent. This year Kham Aid’s wheelchair team met one young paraplegic in Ganzi who had been shot in the lower back while picking yartsa gunbu, presumably on disputed land although details of the conflict were not provided to the wheelchair team.

For a family with many strong pickers, the income from yartsa gunbu can be substantial — upwards of 100,000 yuan ($15,000) or more in a one-and-a-half month season. This is by far the most important source of cash income for most rural families, far exceeding income dericed from itinerant labor or agricultural products. It is probably one reason why the rates for unskilled labor in Kham have shot up from 40 yuan/day to 70-80 yuan/day in the last ten years. Of course during picking season, workers are practically unobtainable.

The importance of yartsa gunbu to the Tibetan economy cannot be overstated and it is certainly a very important factor tying rural Tibetans to their birthplaces. Without yartsa gunbu it is likely that many Tibetans would leave their homes and join the millions of migrant workers roaming around China; others would go into exile abroad. The income produced by worm-gathering is also no doubt an important factor for social stability in Tibet as well as the source of many offerings given by Tibetans to their Buddhist monasteries.

While some fret that the yartsa gunbu is being over-harvested, there are so far no scientific studies measuring the population from year to year to show the effect of gathering. It is conceivable that gathering has no effect on the population because it largely takes place after the reproductive cycle is finished. The sustainability of current levels of harvest is an important topic for research and is not yet resolved.

A collapse of the wild population would be bad, but at least the price would remain high and some collecting would no doubt continue. A far worse development would be if efforts to farm yartsa gunbu in large quantities succeed. This would lower the price of the product and put hundreds of thousands of rural gatherers permanently out of business. Although many entrepreneurs and research institutes are trying to cultivate the caterpillar fungus, no one has yet succeeded in doing so; but the possibility remains a concern.