Driven by the escalating cost of some herbs, harvesting is damaging some fragile environmental areas:

" Yushu and its neighbouring Golog Tibetan Autonomous Prefecture claim the best aweto worms in the country, and as such bear witness to the worst devastation of mountain slopes where it is supposed to grow.

Every year, from April to June, more than 100,000 diggers swarm to the meadows there for the golden collecting season. Eyes peeled to hunt the "soft gold," this digging army leaves behind it slopes peppered with numerous holes that disturb the fragile vegetation of the plateau, where soil can take 10,000 years to become one centimetre thick.

"You didn't see so many people digging here years ago," says Lamo. "Local people have always dug for chongcao traditionally, but not on such a massive scale."

The driving force behind the digging craze is money, says Qiuying Lanze, an official working for the prefecture government of Yushu.

His remark is backed up by Jin Xingqi, an aweto worm dealer based in Xining, the capital of Qinghai. In the 1970s, the government-set purchase price for aweto worms was only 21 yuan (US$2.50) per kilogram, but the price has been soaring since the early 1990s, he says, to 42,000 yuan (US$5,060) per kilogram this year for top- grade herbs. In coastal cities in East China and Southeast Asia, Jin says, it can cost 4,000 yuan (US$481) more."