The Last of the Fungus

Explore

In eastern Tibet, high in the Himalaya, Tenzin stopped at a cliff edge. He lit another cigarette. In front of us, Mt. Gongga dazzled in spring’s morning light, a dizzying 24,800 feet above sea level. Tenzin is not his real name. His perilous occupation—collecting and selling caterpillar fungus—is fraught with competition and secrecy, and I didn’t want to put him in jeopardy with the local authorities.

Tenzin (a common local name meaning “holder of Dharma”) had reluctantly agreed to show me how to find the treasured fungus. He was in his mid-30s and generally taciturn. But his growing dissatisfaction with my ability to keep up on the trek began to show in his furrowing eyebrows. It was 2016, and I was a first-year doctoral student in search of a thesis. I, too, grew up in this part of the world—my hometown in the Sichuan lowland was only a day’s drive away. But I was naive enough to think that training on an elliptical machine was adequate preparation to hunt caterpillar fungus in person. Whenever I fell too far behind, Tenzin sat down and smoked a cigarette in ostensible boredom. 

This parasitic fungus took over the bug’s body and commandeered its brain.

We retreated from the cliff and trekked along steep grasslands. Tenzin stopped at a cluster of dry plant stalks no less than a few inches tall and gestured to me to come over. He pointed to a brown stroma—a bundle of spore-bearing fungal tissue. It looked like a rusted nail sticking up in the soil.

The previous summer, our quarry was an unsuspecting insect spending its larval caterpillar days—on its way to emerging as a ghost moth—in what should be the safe embrace of the earth. Through a process that had remained mysterious, it picked up an unfortunate infection: an insidious and wily fungus called Ophiocordyceps sinensis. 

This parasitic fungus took over the bug’s body and commandeered its brain, maneuvering the caterpillar into the perfect place, just below the surface of the soil, before consuming it from the inside. At just the right time in the spring, the fungus blasted a stroma out of the caterpillar’s head and up from the soil.

Tenzin took out a pocketknife and plunged it into the ground next to the stroma. He excavated the “caterpillar” part of the booty. It was eerie: the mandible, complex eyes, three pairs of prolegs—characters I encountered in my entomology coursework, now real, half-covered in soil and dangled under the stroma. Even the exoskeletal segmentation was clear. But the ex-caterpillar was twisted, a sign of suffering in its previous life; the fungal stroma looked sinister and triumphant. Tenzin protectively wrapped the caterpillar fungus in a home-sewn pouch.

Before sunset, we found more than 30 caterpillar carcasses. We arrived back at his village after nightfall, and Tenzin sold them all to a middleman for $300. Two weeks of unusually good days like this would bring in roughly the average income for a Tibetan household for an entire year.

The fungi would now begin a journey that left the villagers like Tenzin behind. It would trickle through village-level middlemen to the city of Kangding, eastern Tibet’s once prosperous tea-horse trading post. From there, they would be brought to the inland metropolis of Chengdu, China, meeting streams of other caterpillar fungus from other networks that crawl over the entire rugged range from northwestern India to the Qinghai-Tibetan Plateau. Most would be dispersed across the coastal Chinese megacities, where they are sold in herbal medicine markets, high-end restaurants, and caterpillar fungus specialty shops that have the ambiance of exclusive wineries.

Throughout Asian history, caterpillar fungus has been celebrated to have medical and aphrodisiacal powers. Today it’s known as “Himalayan Viagra.” Most modern scientific experimentation has failed to demonstrate any lasting medicinal potency in the fungus, but its roots in culture and tradition have proven nearly impossible to break. Demand for it is insatiable.

To feed this hunger, some 100,000 kilograms of dry caterpillar fungus are harvested along the Himalaya each year.¹ This means more than 300 million caterpillar fungi are hand-picked annually from the world’s rooftop. Market price of caterpillar fungus equates to a full tenth of Tibet’s gross domestic product—more than its mining and other industrial sectors combined. With this amount of money, stakes are high; not far from Mt. Gongga, armed conflicts have broken out between rival villages for access to good caterpillar fungus habitat. 

Competition for this limited but naturally renewable resource is poised to escalate. Caterpillar fungi grow in vulnerable alpines of the Himalaya and Tibet. Scientists predict a 1.1 degree Celsius temperature rise in these habitats over the next decade, which will significantly reduce caterpillar fungus yield, and force collectors to less-accessible, more dangerous, and more fragile higher elevations.

One way to prepare for this ecological and economic doomsday is to try to cultivate the fungus, putting the vagaries of nature under control and, potentially, at scale. But caterpillar fungus, it turns out, is not a simple crop to sow, or animal to husband. It is a complex and intimate and tricky organism, whose life cycle and infection pathways have eluded scientists for centuries.

Over the course of seven years and thousands of rugged miles, I intermittently followed Tenzin and other treasure hunters on the fevered trail of the caterpillar fungus. Along the way, I worked on my Ph.D. in biology at Harvard University, probing the mysteries of the caterpillar fungus. I hoped to uncover a solution to avert the disaster I saw looming for the millions of rural Tibetans whose lives depended on it.

In 2017, I drove to a humble-looking agricultural operation in eastern Tibet’s mountain valleys. It might have been mistaken for yet another roadside strawberry farm; in fact, it was an experimental caterpillar fungus breeding center. Darong Yang was expecting me.

Darong had first learned about caterpillar fungus in the 1970s when, as a college student, he was dispatched to a military encampment near the border with Burma, another hotspot for the cold-adapted fungus. After working at the Chinese Academy of Sciences and a long career in insect taxonomy studying host moths of caterpillar fungus, he decided to go commercial. 

Caterpillar fungus has been celebrated to have aphrodisiacal powers. Demand for it is insatiable.

Earlier in the year, his breeding center had struck tentative gold: He cultivated one kilogram of caterpillar fungus. It took Darong his entire academic career to figure out the pieces of a viable breeding scheme. He bred the ghost moths, collecting the eggs—some 300 for each female moth. These eggs are isolated in a pupal growth chamber and hatched under strict, sterilized conditions. Once the millions of caterpillars are just the right age, a few are selected to become breeding moths, and the rest are treated to a shower of O. sinensis spores. Then Darong prays that his caterpillars are infected. His prayers are rarely answered.

That came as a surprise to Darong—and most anyone else tracking this fungus. In their natural habitat, about 10 percent of underground ghost moth caterpillars are infected with O. sinensis. Bringing caterpillars into captivity and assaulting them with a salvo of highly concentrated spores resulted in 10,000 times fewer infections. It took Darong about 5 million caterpillars to produce that one kilogram of caterpillar fungus. It was enough to generate interest, but far from enough to fundamentally change the livelihood of millions of people.

And Darong’s is one of the most successful operations. In the past decade, some 20 caterpillar fungus breeding centers have sprung into existence across China, many government-funded or university-affiliated. None has achieved an infection rate even close to that effortlessly accomplished in nature.

Each year, breeding centers have to cycle through hundreds of millions of ghost moth caterpillars, like lab rats, to test new infection strategies. However, most centers did not invest in the technical expertise and infrastructure to maintain a sustainable host moth population like Darong does. Instead, they rely on a more immediate way to source their test subjects: digging them out of their grassland homes.

As someone studying entomology, I knew there was a crucial difference between harvesting caterpillar fungus and harvesting caterpillars. Infected caterpillars are essentially dead ends; collecting them is harvesting something that is, in a sense, already gone. Live caterpillars, on the other hand, are essential for population renewal—and thereby, caterpillar fungus generation. Because these live caterpillars are so multitudinous (in the right habitat), uprooting them also means decimating vast areas of pristine vegetation that is already under strain from rapid climate change. 

Being so essential to the region’s economy, these breeding efforts are backed by major cash. Breeding center representatives will arrive in a village and offer high prices for live caterpillars, leading to a local “caterpillar rush” on their habitats. By the next year, villagers will see a devastating decrease in their caterpillar fungus yield. By then, of course, the cunning representative would be long gone.

My academic research in the lab, half a world away, kept leading me back to one vexing question, one that required me returning to the source for the answer: How, exactly, were the ghost moth caterpillars becoming infected in their natural habitat? This knowledge could increase yield and reduce the back-breaking, and sometimes deadly, work collectors like Tenzin had to endure.

Later in 2017, I headed back to Mt. Gongga with my questions, but Tenzin had no time for my grand gibberish. Coinciding with my visit, a breeding center representative was offering villagers $1 for each live ghost moth caterpillar exhumed from the Yanzigou—the highest yielding habitat around Mt. Gongga. It seemed like the entire village was digging in, shoveling bucket loads of tundra soil and picking out anything that wriggled. This time, Tenzin did not bring the home-sewn pouch as he would for fungus collection; he carried a big shovel and plastic water bottles for his live captures.

Armed conflicts have broken out for access to good caterpillar fungus habitat.

In twilight, dozens of people crowded into a dimly lit shack behind the local convenience store, where the representative counted live caterpillars by hand, tossing them into a large water bucket. The congregation was hushed (and I would like to think, slightly mollified—though I couldn’t discern anyone’s face in the shadows). The cash-only transaction was swift. I stayed to observe the full count: 20,000 live caterpillars dug out of the soil in a single day. 

In the course of a few weeks, I saw villagers turn the delicate montane ecosystem, with its succulent and radiant flowering plants, upside down like an apocalypse in fast motion. Alerting the forestry official was useless (and it was never a good idea to meddle with village politics). Instead, I preached biology to anyone who would listen—drawing life cycle diagrams to show that there won’t be caterpillar fungus next year if they dug out all the caterpillars now. But what eclipsed reason that summer was a tragedy of the commons. Tenzin told me that if they didn’t dig, villagers downstream would beat them to it. 

All the while, these tens of thousands of live caterpillars would go on to breeding centers only to likely elude fungal infection. Their lives were, by a twist of still-mysterious ecology, spared from that fate. But their futures augured an increasingly bleak outlook for the village.

Back in the United States, in the lab, I began to formulate an idea as to why the efforts to infect caterpillars in captivity were failing. Having grown up collecting insects and keeping quite a few of my own “trade secrets” about their whereabouts, I grokked that habitat is more than a bug’s residential address: It’s where it eats, mates, and encounters predators and prey; it’s the tangled bank and the web-of-life. Extracting a species from its habitat is an oxymoron, like asking us to live without eating and breathing. 

Parasitism, I reasoned, also depends on habitat. When a zombie ant, for instance, is possessed by a fungus (Ophiocordyceps unilateralis), the ant will climb to just the right spot on a tree and clamp its jaws on the underside of a leaf. From this advantageous position, the fungus pushes a stroma out of the now-deceased ant’s head and rains spores onto more unsuspecting ants below. The fungus’ reproductive success depends on the abundance of its hosts. There is no dearth of ants in the rainforest, so showering them with airborne spores makes evolutionary sense.

But this is not the case for O. sinensis, whose infection target, the caterpillar, prefers to live about a foot underground—and spore density of O. sinensis is negligible this deep in the soil. So how did symbiosis with a host playing hard-to-get arise in the first place?

What if plants, I thought, were the true hideout of O. sinensis? Caterpillars are, in a way, just squishy, salad-loving automatons. This hypothesis explained how the caterpillars were becoming infected: Caterpillars evolved to eat plants, and what better way to infect them than by poisoning their food? The hypothesis also explained why infection in captivity had been so elusive. Removing wild vegetation in captivity cut off the evolved pathway of fungal infection. 

To test this hypothesis, I returned to Mt. Gongga in 2018. I managed to talk Tenzin into being my guide again—I promised not to slow him down. This time, we had to trek farther up the glacier to find caterpillar fungus, since most habitats had been decimated the previous season in the mad rush. Villagers were visibly moody about the decreased fungus harvest. Before my arrival, one of them, looking for a better yield, risked the steeper side of the valley, lost his footing, and fell to his death. Most villagers believed karma was responsible. Following the accident, village elders removed wooden planks across ravines to close off the mountains. I, having played Cassandra the previous year, was granted the last passage.

Amid the grasslands, my plan was simple. If O. sinensis lived inside the plants, I should be able to detect it there. With Tenzin leading the way, I collected 690 samples of leaves and roots from the 27 plant families in the habitat. I then drove them straight to the nearest molecular lab, nearly 200 miles away. I sterilized and smashed each sample for analysis. To study them, I developed molecular “probes” that would only bind to a fragment of the O. sinensis genome. Whenever this binding occurred, a beam of fluorescent light shone and could be picked up by a sensor.

Later, I headed back to Mt. Gongga with my questions, but Tenzin had no time for my grand gibberish.

The results were unequivocal: More than one in three of my plant samples contained O. sinensis. And after analyzing the ooze from 73 wild-dwelling caterpillars from the same habitat, I found in their guts not one but 11 different plant families they’d eaten that harbored O. sinensis. The caterpillars were indeed most likely munching their way to infection.² 

That meant, I realized, the current attempts to domesticate caterpillar fungus were a futile endeavor. Those millions of displaced live caterpillars, those acres of demolished delicate herbage were all for naught, because captive breeding excludes the main pathway of O. sinensis infection: eating local plants. 

But another idea began taking shape in my brain, one that would make cultivating the fungus even more difficult. Parasitism is not a static process. Hosts and parasites coevolve. If a speciation event occurs and causes a single host species to diverge into two, its specific parasites would split, too. This can lead to a permanent break between a species and its parasite. If the caterpillars and parasites were in the midst of a wide-scale speciation event, it wouldn’t work to randomly pick caterpillars and fungal strains. Every person involved in the breeding efforts, from villagers with their shovels to breeding center directors with their cash, would be trying to start a motorcycle with the wrong key. Maybe, I thought, I could help find the right one.

Taxonomists, including Darong the breeder, had already noticed regional differences in some of the physical characteristics of adult ghost moths. Cutthroat caterpillar fungus traders often cite exoskeletal color and size to vouch for the authenticity and provenance of their products. Coevolution, I realized, could very likely have occurred across this vast habitat, which is roughly the size of Alaska and fragmented by the world’s tallest mountains—ideal conditions for speciation by geographical isolation. 

Back at Harvard, I started to build molecular phylogenies for the fungus and caterpillar, neither of which had been done at this sweeping scale. While it was relatively easy to extract fungal DNA from dried caterpillar fungus, recovering usable host DNA turned out to be a major hurdle, since much of the arthropod is consumed during parasitization, leaving little insect material to work with. I turned to a technique called hybrid enrichment, which was first applied to sequencing ancient Neanderthal genomes from degraded samples. If the protocol worked with prehistoric bone fragments, I figured, it could work with dried caterpillar fungi. I spent a year isolating and amplifying the DNA in my lab. Patience was key: I learned to time defrosting reagents just so, to inhale and exhale at just the right moments while pipetting, to establish order among the hundreds of plate wells. Eventually I had a working method, and fragmented pieces of caterpillar genome could be restitched together. 

It was time to take to the road again and collect caterpillar fungus across the vast Himalaya.

In spring 2019, I arrived at a monastery in Kathmandu, Nepal. I wanted to brush up my Tibetan and glean information from local caterpillar fungus sellers and collectors. One of the caterpillar fungus shops I frequented was next to the Russian Embassy, where I motorcycled back and forth after my afternoon language drills. For a while, rumors along the plotline of Rudyard Kipling’s Kim started to circulate among my peace-loving monastic peers. Was I some kind of undercover agent? But my persistent explanation—I’m here to study how zombie caterpillars evolved—eventually left them with no doubt that I was more of a quixotic wanderer than a serious security threat.

Then I took to the terrain, to hunt down these caterpillars across their range—and with them, the steps of their evolutionary dance with a microscopic predator. 

My first stop was the foothills of remote Namcha Barwa, the mountain which looms above at 25,500 feet. Reaching these rich collecting sites required traversing dense, sub-tropical thickets reigned by legions of leeches. 

With ounces of my blood left behind, but crucial samples gained, I proceeded west along the Tibetan borderline with Bhutan, Sikkim, Nepal, and northwestern India. I asked villagers to bring me caterpillar fungus (chong-cao, yartsa-gunbu, or keera-jhar, depending on where I asked). Kind stakeholders in this contentious work were usually willing to spare me a few stalks—key data points in the vast trading web spanning almost the entirety of eastern Asia.

I had some trouble on my last stop, though, in the Himalayan ranges of northwestern India, one of the most recent regions to join the “caterpillar fever.” Again, I was accused of espionage (the Chinese fighter jets constantly patrolling the distant skyline did not help assuage local worries). Luckily, some collectors happened to be college students trying to make a few bucks during their summer break, and I explained to them my project of making a “family tree” of the caterpillar fungus. They gifted me some of their harvest and befriended me on WhatsApp.

While I was behind the wheel along heart-stopping roads in the high Himalaya, collaborators scoured the northern and eastern edges of the Tibetan Plateau. They delivered caterpillar fungus tied up with foul-smelling yak hair—the way these bounties were packaged centuries ago. I even salvaged a few rare samples soaked in Darong’s alcohol concoction (one of two popular ways to consume them in China; the other being stewed in chicken broth).

Back in the lab in Cambridge, samples isolated, enriched, reassembled, and sequenced, a geographical and evolutionary map of these prey-parasite pairs began to come into focus. Among the 93 caterpillar-fungus samples, I found that at least 20 different species of caterpillars and six separate strains of the fungus have coevolved. It turned out that a caterpillar fungus collected in Qinghai is vastly different from one collected in India. Even ones from the eastern and northeastern parts of Tibet, sites within a few hours’ drive, fell into separate genetic groupings—incompatible with each others’ intimate nemesis. My survey, despite the mileage, covered only a fraction of known caterpillar fungus collection sites. Mountains are biodiversity hotspots, and the true tally of matching host moth species and fungal strains across the Himalaya is likely far higher. In other words: There were so many keys and so many motorcycles—any selection seemed unlikely to match. 

This discovery was a final nail in the coffin of current caterpillar fungus breeding efforts. If perhaps dozens of different caterpillar species were each locked in a unique arms race with their own fungal strain, then showering caterpillars with a single fungal strain might be completely useless if they are mismatched. A breeding scheme without consideration of coevolved host-specificity is a waste of time, money, and, in this case, an increasingly scarce natural resource.

In 2022, I published these findings in the Proceedings of the Royal Society: Biological Sciences, which would have been impossible without the help of Tenzin and countless local collectors like him.³ But at a personal level, I had failed them. I had wished to alight on some ecological insight that would liberate them from senseless travail and ecological wreckage; instead I revealed the precarity of living off the land, and the inevitability of the decline of their livelihood if the habitat continues to deteriorate. Even that was a generous impact statement; in all honesty, apart from a few academics (who enthusiastically informed me that their insect-devouring fungus was also plant-dwelling), my research was largely overlooked. Live caterpillars were still being excavated in the name of experimentation. Pristine alpine meadows were still being devastated.

More than 300 million caterpillar fungi are hand-picked annually from the world’s rooftop.

This summer, I returned to the region, visiting traders in the Tibetan capital of Lhasa. In the caterpillar fungus boutiques of the old city district, we exchanged butter tea and the ups and downs of this year’s business (the price was up again). Since I posted all the genetic markers of caterpillar fungus online, Lhasa traders have braced for a future when they might have to use genetics to authenticate their product. I have stayed clear of any business interests but, even with my Ph.D. work published and wrapped up, I continued to be enthralled by this cultural obsession that props up an entire economy. Some of the traders I interviewed had been dealing caterpillar fungus for three generations, and so had their suppliers in the nearby mountains.

It is possible that caterpillar fungi are still hiding some irreplaceable remedial property—stories abound of medicinal discoveries from traditional or indigenous plants and fungus—but as of now, that science remains null. The industry simply reminds me of the 17th-century Dutch tulip fever and the tragically ongoing ivory craze. I’m in no position to advise local stakeholders on how to make their living, which only leaves me with a spectator’s anxiety. 

Not all hope is lost for caterpillar fungus cultivation. The interdependent life of the fungus points to a new means to farm it. Breeding centers can’t be industrial sow-and-reap operations. They must consider ecological and evolutionary factors. Breeding must be situated where the fungus naturally grows—on undisturbed, high-elevation, microbe-laden soil. Yield will boil down to the land’s carrying capacity, to how many caterpillars nature can support, without breaking the equilibrium among plants, insects, and fungi. Breeding centers would look more like conservation land than industrial farms or scientific laboratories. The future of the caterpillar-fungus harvest—a feature of Tibetan culture for five centuries—should look much more like the past. It could again thrive, not in a beaker, but in preserved, existing habitat.

In a 15th-century medicinal text, “An Ocean of Aphrodisiac Qualities,” Buddhist lama and physician Nyamnyi Dorje praises the caterpillar fungus in what reads like a hymn:

It grows in beautiful mountain regions
On remote grass-covered slopes.
In the summer it is a blade of grass on a worm
Similar to the leaf of mountain garlic.
The flower resembles a silken green sedge.
The root resembles cumin seed at the end of autumn …
It is a faultless treasure of an ocean of good qualities.

Throughout my journeys, I often thought of Nyamnyi Dorje. I imagined him in red robes, kneeling piously to observe the fragile stroma he uncovered one summer evening, jotting his thoughts down on the fragrant pages of a string-bound pecha. I long for an opportunity to converse with him and tell him what I’ve discovered, and what I hope for this region. When I play this scenario in my mind, Nyamnyi Dorje listens patiently, offering more butter tea as I talk. When I finish, he smiles and says only one word: o-ya. It means: good, of course.  

Zhengyang Wang is a writer and conservation biologist who uses emerging technologies in molecular ecology and remote sensing to monitor insects across the landscape.

Lead photo: Local caterpillar fungus collector Tenzin treks near the Yanzigou glaciers, more than 12,500 feet above sea level, to seek the the telltale stroma of the fungus. The glaciers are melting, and the land is warming, threatening this precarious industry. Credit: Zhengyang Wang.

References

1. Winkler, D. Caterpillar fungus (Ophiocordyceps sinensis) production and sustainability on the Tibetan Plateau and in the Himalayas. Asian Medicine 5, 291-316 (2009).

2. Wang, Z., et al. The entomophagous caterpillar fungus Ophiocordyceps sinensis is consumed by its lepidopteran host as a plant endophyte. Fungal Ecology 24, 100989 (2020).

3. Wang, Z., et al. Profiling, monitoring, and conserving caterpillar fungus in the Himalayan region using anchored hybrid enrichment markers. Proceedings of the Royal Society: Biological Sciences 289, 2021650 (2022).

• Zhengyang Wang

  Posted on August 30, 2023

Get the Nautilus newsletter

Cutting-edge science, unraveled by the very brightest living thinkers.

Newsletter Signup – In Page Mobile

Email: *

Captcha

If you are human, leave this field blank.

Sign up for free