Climate change and overharvesting have put a Himalayan fungus valued for its purported aphrodisiac qualities at risk of extinction.

Known variously as yarsagumba, yarchagumba, yartsa gunba, yatsa gunbu and, more colloquially, "Himalayan Viagra," the parasitic caterpillar fungus Cordyceps (Ophiocordyceps sinensis) grows on and kills Tibetan ghost moths during their larval phase underground. A tiny mushroom sprouts from the head of the dead larva, poking a few millimeters out of the ground. Traditional Chinese medicine (TCM) claims the funguswhich is boiled and added to tea or soupcan act as an aphrodisiac, cure cancer and fight fatigue. These medical claims have not been borne out scientifically.

Although the fungus has been used in TCM for centuries, demand took off after 1993 when three female Chinese runners broke world records and their coach told the media he had fed the athletes yarsagumba in a soup of turtle blood.

Yarsagumba is harvested by Nepalese villagers who sell it for more than $25 a gram (retail prices soar to $150 per gram or more). But as Agence France-Presse (AFP) reports, the growth in demand has made yarsagumba supplies scarce. Villagers who once collected 150 to 200 pieces of the fungus in a month are now only finding only 10, 20 or 30 pieces. AFP also cites climate change as a possible reason for shrinking supplies. The regions where the fungus normally grows have experienced lower levels of snow and rain as well as higher temperatures in the past few years.

Caterpillar fungus store in Lhasa, Tibet Autonomous Region, People's Republic of China. By Erik Trner via Flickr. Used under Creative Commons license

One of the few actual studies of O. sinensis is being conducted by Uttam Babu Shrestha, a PhD student at the University of Massachusetts Boston. Shrestha found that the villagers who harvest yarsagumba live in mountainous regions that contain few natural resources and where agricultural productivity is low, making the fungus their primary source of income. In a project synopsis for a study funded by The Rufford Small Grants Foundation, he wrote that the depletion of the fungus would severely impact the economy and culture of the people who rely on it. The study, published February 1 in Nature, calculated the global market for yarsagumba to be between $5 billion and $11 billion. (Scientific American is part of Nature Publishing Group.)

A 2008 study in Economic Botany found that fungus collection represented 40 percent of the rural cash income in the Tibet Autonomous Region, China, where it is also collected.

Shrestha is currently in Nepal's Dolpa District, which provides more than half of China's yarsagumba. He told AFP that 5,000 people have come to Dolpa this year to search for the fungus in 16 pastures, which are open from April to June, "but they haven't found any."

Shrinking supplies and high prices have also led to heightened tensions among fungus hunters, who pay nearly $100 each for annual collection licenses. Seven Nepalese men were found dead in 2009, possibly murdered for their yarsagumba.

Photo by William Rafti via Wikimedia Commons. Used under Creative Commons license