a fungus growing out of its face.

I’m Anna, and this is Gross Science.

On the Tibetan Plateau and the Himalayas, ghost moth caterpillars live underground,

keeping warm and eating plant roots til they turn into adult ghost moths.

That is, unless they get infected with the fungus Ophiocordyceps sinensis. The fungus

enters a caterpillar’s body in summer or autumn, and it starts to grow in threads through

the caterpillar’s organs, eating it from the inside out. Brainwashed by the fungus,

the caterpillar crawls upward until it’s just below the surface of the soil, where

it dies.

In the spring, a long, brown fungal stalk bursts from the caterpillar’s head. It pops

through the soil to send out its spores, which infect other caterpillars—and the circle

of life and parasitism continue.

Now, you might think that’s the end of the story, but people scour the meadows where

the fungus grows, hoping to harvest these infected corpses. Why? Well, a pound of the

fungus, called yartsa gunbu, can be worth tens of thousands of dollars. In fact, it’s

probably the most valuable fungus in the world. That’s because it’s used in traditional

Chinese and Tibetan medicine to slow aging, cure cancer, and treat all kinds of other

diseases. It’s even sold as an aphrodisiac.

The science is still out on whether eating yartsa gunbu actually does anything good for

your health. But, harvesting it is definitely bad for the fungus. It’s a huge status symbol

in China, and people have collected so much Ophiocordyceps sinensis that it’s now endangered

in some places.

And, this isn’t just a problem for the parasite, or for the people who eat it or brew it in

tea. Yartsa gunbu is a big part of the economy in places where it’s harvested, like Tibet

and Nepal. So, local communities are trying to figure out ways to sustainably harvest

the fungus. Because for them, this is one parasite that’s worth protecting.

I still feel kind of bad for the caterpillar though.

Ew.