Winter Worm, Summer Grass

The best caterpillar fungus is found at higher elevations, places such as Heitushan, the 14,000-foot Black Earth Mountain in Golog where Lhamotso lives.

Lhamotso counts herself lucky to have the motorcycle to climb the mountain. She works alongside her daughters bringing down the fungus a little every day.

Although the dead caterpillar is rather unprepossessing in appearance, it’s not nearly as disgusting as it sounds: sort of like a little yellow root with a stalk growing out of the top. Reaching into the pocket of her faux leather jacket, daughter Hiriti pulls out a tissue and unwraps what looks like a 3-inch-long twig, the only piece she found all day. It will sell for about $3, but it could command a retail price of $10 in Singapore or Tokyo.

Lhamotso is well aware that fungus might not be a reliable source of income for much longer. The fungus is growing scarcer from over-harvesting and changes in the fragile ecosystem of the Tibetan plateau.

''For years, it’s been like digging up gold but more valuable,” says Daodu, 31, a teacher. “People today can’t survive without it.”...