A parasitic fungus that infects caterpillars in the Himalayas had been a fixture in traditional Chinese and Tibetan medicine for centuries, but overharvesting and a warming climate has put the unique organism – and the people who depend on it for their livelihoods – in jeopardy.

Harvested after the fungus has incapacitated the ground-dwelling moth larvae yet before it has released its spores, Ophiocordyceps sinensis – known locally as "yarchagumba" – is highly sought after as a treatment for a number of wide-ranging conditions, including cancer, asthma, kidney disease, toothaches, and high cholesterol. Its most popular application, as a supposedly potent aphrodisiac, has lent it the nickname "Himalayan viagra".

According to a team of researchers from Stanford University and Colorado State University, the demand for yarchagumba has increased in the past few decades due to a growing market for traditional medicines in Chinese urban areas. They note that price per kilogram has surged by about 20 percent per year from 1997–2012; as of 2017, the fungus was worth three times its weight in gold.

“Himalayan caterpillar fungus has become one of the world’s most valuable biological commodities,” they wrote in the Proceedings of the National Academy of Sciences, “providing a crucial source of income for hundreds of thousands of collectors.”

However, assessments into the current state of the caterpillar fungus have been limited, and no investigations have looked into the effects that climate change may have already had. The team’s study sought to remedy this gap in knowledge.

Using interviews with 49 caterpillar fungus collectors, traders, and community leaders in the Himalayan region of China and the Tibet Autonomous Region (Tibet), reviews of 29 scientific publications, official collection records, and regional climate data, the researchers were able to confirm their suspicions.

“Our multiple evidence base approach using data spanning nearly two decades and four countries revealed that caterpillar fungus production is declining throughout much of its range," they wrote. "While collectors increasingly attribute the decline in caterpillar fungus to overharvesting, habitat and production modeling suggest that climate change is also likely playing a role.”

The fungus, which has evolved to grow inside the bodies of 50 species of Thitarodes moth, is only found in a small sliver of the high-elevation Tibetan Plateau where winter temperatures drop to well below freezing but the soil thaws during spring and summer. Climate data shows that winter temperatures warmed significantly from 1979 to 2013 across much of the fungi’s range, particularly in Bhutan, where increases averaged 3.5 to 4°C. Such dramatic habitat shifts likely suppressed the fungal population by affecting the moths and the plants that the moths rely on.  

"[T]his study could serve as a warming of what many harvesters already realize," lead author Kelly Hopping told AFP. "That decreasing availability of this fungus will be devastating to local economies, and that these communities need other viable livelihood options."