This is the yarchagumba picking season, and across Dolpa district schools are empty, government offices are deserted. Just about everyone has gone up the mountain to see if they can pick the mysterious half-caterpillar-half-mushroom known as Himalayan viagra.

"Yarchagumba cures headaches, stomach aches, many diseases. You'll get lots of energy," Chandra Shahi explains. Then he leans across and whispers: "It's also good for.if a man doesn't feel like sleeping with his wife anymore he should definitely try yarchagumba."

By the end of May every year, some 30,000 people in Dolpa set off to find yarchagumba. The season lasts until the end of June. "It's an unofficial holiday,"says Narayan Parajuli. "I have only 10 students out of 65, most of them are out searching for yarchagumba."

Yarchagumba is known by its Latin name Cordyceps sinesis and is a unique combination of a yellow caterpillar and a mushroom. Few scientists have studied the phenomenon, and its lifecycle is not completely understood. The Tibetan name means 'summer grass, winter insect'. Just before the rainy season, spores of the cordyceps mushroom land on the heads of caterpillars of the Lepidoptera family that live mainly underground. After the fungus buries itself in the caterpillar's body, it works its way out through the unfortunate insect's head. The parasite soaks up the caterpillar's energy until it dies. Yarchagumba can be found when the snow starts to melt between 3,300-4,000m in parts of Tibet, India, Bhutan and Nepal.

"When Dolpa people find yarchagumba, they don't find a caterpillar, they find money," Chandra Shahi tells us. "Last year I made Rs 50,000. Even kids were making Rs 2,000 per day." This is big money in one of Nepal's more remote and rugged areas.

It is an intricate network of Kathmandu investors who finance local businessmen who in turn hire subcontractors or buy yarchagumba directly from gatherers. "Everybody who has a lot of money in Dolpa is involved," Dipendra Shahi, a local businessman told us. This year the yarchagumba is bought from collectors for Rs 120,000 per kg. Depending on quality and size of the product, the middlemen sell the stuff by the sackload in Thailand, Korea, China and Japan for $2,800 per kg. The Western market is also said to be getting bigger. Japanese scientists, who first came to Dolpa's mountains in a helicopter, have even tried to grow yarchagumba back home in refrigerators to simulate Himalayan conditions. It didn't work.

Until recently, collecting yarchagumba was illegal in Nepal. That changed two years ago, when the government allowed collection of the precious caterpillar-mushroom outside of the Dolpa National Park boundaries. The government wanted a share of the lucrative pie: businessmen now need a permit and the government collects Rs 20,000 tax per kg. However, most businessmen say they sell the yarchagumba directly to Tibetan traders, who come to buy the goods in Do Terab, Upper Dolpa.

"The tax is way too high," a businessman from Dunai says. "This year we might have to use official channels and send the yarchagumba to Kathmandu, because the border is closed for Tibetans because of SARS. But we'll probably first wait and see, keep our goods in stock for a while."

Walking up the small trail from Dunai to Thaage Lekh, an area near the Rukum border, there is a lot of to and fro of fortune hunters. Many are from Dolpa, but some are from distant districts, carrying baskets with tents and food. People going up are generally in a far better mood than people coming down. "I'm going home," says Bahar Rawal from Jajarkot. "Everybody told me: go to Dolpa, you'll make lots of money." He took a loan and walked for six days, his food is finished, and he found only three pieces in three days. "I'm in big trouble," says Rawal.

The Dolpali don't like the invasion of their district by groups from other districts, but the outsiders have the protection of Maoists. "Everybody has the right to collect yarchagumba," Comrade Leknath explains. The Maoists allow the Dolpali to collect a Rs 100 fee from the visitors, but if a collector finds only a very few yarchagumbas the Maoists force the VDC to refund the money.

The Maoists collect their own tax as well and are competing with the government to control as much of the business as possible. In order to bring a bigger area under their influence, 150 of Dolpa's 500 armed Maoists went to Do Terab in Upper Dolpa at the end of May. The Maoists say they have a tendering system: businessmen who want to buy and sell yarchagumba have to pay a Rs 20,000 advance. If the Maoists find a trader without a permit they loot his yarchagumba.

In addition, they have to pay Rs 5,000 per kg. Maoists buy yarchagumba directly from freelancers as well for a fixed price of Rs 30 per caterpillar and sell it back to businessmen. "We use the money to pay for our armed forces and cultural programs, since we no longer take donations from locals," Comrade Leknath explains. The Maoists have also been collecting $100 from every trekker entering the Dolpa region, and their collection point is only 100m from the security base at Jufal airfield.

Porters on the caterpillar trail.

At a camp on Taaghe Lekh (4,200 m) the sun goes down. It is quickly getting cold and everybody sits around campfires. The atmosphere is cheerful. People drink 'Tibetan water' (raksi), listen to the radio, and dance in a big tent in the middle of the camp. They talk about the necessity of peace and, inevitably, about yarchagumba.
"A week ago there were more then 200 tents here," Sher Bahadur Shahi says. "Many people have gone to try their luck somewhere else." The next morning the remaining group leaves early with their sickles. Near Jangala Pass (4,500 m) small dots of people are scattered across the flanks for the mountain. On hands and knees they go through the ground on all fours looking for the small brown stalk of the yarchagumba mushroom that sticks out of the ground.

"Last year we found many yarchagumba here," Chandra Shahi says, his eyes focussed on the slope. This year, the catch is poor. Some believe it is because there has been too much snowfall. Others think too much was collected last year. And that is also what national park rangers are worried about: if picking goes on at this rate, yarchagumba may be driven to extinction. The gatherers also disturb the park vegetation and leave trash.

At Tarakot, a conspicuously dressed man named Purna Buda has just arrived from Kathmandu. Sitting under his umbrella, Buda relates how he discovered yarchagumba in Dolpa ten years ago. "After a friend told me about yarchagumba I went to Lhasa with samples. The first year I sold 16 kg for Rs 12,000 per kg. The second year I collected 85 kg." Buda hasn't looked back since, and he swears by the aphrodisiac value of the caterpillars. His method: take 30 or so yarchagumba, dry them, keep them soaked inside a bottle of local raksi for a month then drink the raksi every day for a fortnight. "It works for me," he says.

No one really knows whether yarchagumba has aphrodisiac value. But when belief in traditional medicine is so strong, that is really not important. For an area of Nepal where there are no roads, no jobs, and hardly any agriculture it is just another cash crop.