Every summer since he was 18, Ma Youcai has combed the craggy, barren slopes of the mountains that surround his village in rural Qinghai province for dongchongxiacao, a rare, insect-like fungus used in traditional Chinese medicine (TCM).

Dongchongxiacao is a rare, insect-like fungus used in TCM. [China Daily]

A parasite that attacks and eventually kills moth larvae on the Qinghai-Tibet Plateau (it looks like a brown twig growing out of its caterpillar host), just a few grams of the fungus can be ground into powder and dissolved to make a tonic that is believed to boost energy and sexual performance.

But as Ma prepares for yet another summer search, the 40-year-old goat herder fears this valuable fungus, which provides almost half of his annual income, is in danger of disappearing forever.

Last year, he found only half as many fungi as he did a decade ago. In some areas, the population has dropped almost tenfold in the last five years, according to Guo Jinling, an expert on medicinal plants and a professor at the Chengdu University of TCM.

"The price is going up and more people want to make money, so more and more people come to dig for it," said Ma. "There are less and less every year. I'm worried that eventually they will disappear completely."

Scientists say the decline is largely due to habitat loss and over-harvesting, which is being driven by skyrocketing demand for costly and exotic herbal remedies among China's growing middle and upper classes. "Animals and plants need time to grow. When demand causes them to be harvested too fast, they can't keep up and their populations decline," said Long Chunlin, a professor at the Kunming Institute of Botany in Yunnan province.

The problem extends far beyond caterpillar fungus, however. An estimated 15 to 20 percent of plants and animals used in TCM are endangered or near extinction because of over-harvesting and habitat loss, according to a 2008 report by UK-based TRAFFIC, a non-governmental group that tracks wildlife trade.

"Today, Chinese medicine is a big profession with medical schools, universities, hospitals, research institutions and manufacturers," said Lixin Huang, president of the San Francisco-based American College of TCM. "The demand for this medicine has become a challenge, and the demand on plants and animals has become a challenge."

Perhaps the most famous victim of TCM is the tiger. While there are only about 50 tigers left in the wild in China, largely because of reductions to their natural habitat. Other animals whose parts are believed to have medicinal properties, including the Asiatic black bear, saiga antelope, and some turtle and snake species, have also suffered declines in population.