Most people don’t spend a lot of time thinking about fungus. If you’re not using mushrooms in your dinner, and you’re not cleaning up mold somewhere, it’s probably not big on your list of priorities unless you’re stress‑watching The Last of Us. But there’s a lot more to fungus than most of us realize. In fact, it’s a lot more fungus than most of us realize.

what can mycelial networks achieve?

1. Is It All Real?

Not everyone agrees with the concept of a “wood wide web” and the overall influence or benefits of a mycorrhizal network. Dr. Justine Karst, an expert in ectomycorrhizal ecology, believes there’s more fiction than fact in what these networks can do, at least in terms of what has been reported. Karst has contested claims that the networks benefit connected trees and seedlings, citing a lack of any real hard evidence.

Also suspect in Karst’s view is the idea that mycorrhizal networks are as widespread as has been suggested. Too few forests have been mapped to make this conclusion, and only two studies have even suggested the existence of a network without enough data to support a beneficial symbiosis theory.

Karst went on to challenge the idea, which we mentioned earlier, that the networks bring nutrients to all the linked trees, including saplings. In fact, there’s as much evidence that being connected to a network would harm these seedlings as benefit them.

A third claim, which relates to the one regarding tomatoes from earlier, suggests that trees can send warning signals through the network to let other trees know of a dangerous insect infestation, allowing uninfected trees to start producing defensive enzymes. And while that sounds amazing, Karst says that claim has never been backed by a single peer‑reviewed, published study.

Karst is not dismissing the idea that these networks exist or that they may have benefits, just that we shouldn’t be so quick to believe everything we read when all the evidence to support it isn’t necessarily there. And besides, there is plenty of evidence for many of the remarkable things we know about mycelial networks, and certainly enough to encourage people to want to research more deeply and find out the truth about these complex organisms.

2. Tree Connections

Mycelium is integral to forest health. Fungus is able to break down organic matter and ensure soil stays healthy for other organisms to grow by returning nutrients as part of the carbon cycle. They are also crucial to some other plant reproduction, like orchids, for instance. If a very specific fungus is not present in the roots of these orchids, they cannot reproduce at all, making this the most dire form of symbiosis. The plant and the fungus literally need each other to survive.

Some other species of plants, like pinesap, have evolved to no longer rely on photosynthesis but have the fungus connecting them to provide the energy they need to survive. In fact, over 90% of all plant life relies on a symbiotic mycorrhizal network of some kind. If it weren’t for fungus, our world would look vastly different.

The idea that these networks connect and benefit trees and other plants has been proposed and observed by many naturalists, doctors, ecologists, and foresters.

3. Unique Mycelial Capabilities

People have long held that plants and music have a relationship, but this is typically related to things like houseplants and the idea that certain kinds of music make them grow better. There isn’t a lot of conclusive scientific data to support that, although there is some that suggests certain vibrations can either help or hinder the growth of plants. Fungus, as it happens, operates similarly.

Fungus can convert sound waves into electrical signals. This can help in fungal growth as well as development. The electrical pulses were measured and converted back into sound by the Octopus Project, a group of musically inclined scientists, which allowed them to record what is essentially music played by mushrooms. You can find some samples of it online where mushrooms like shiitake and others have been recorded.

As interesting as it is that fungus may respond to sound and even produce its own, there are greater implications. If the sound promotes growth, then it’s been theorized that every plant in the mycorrhizal network could benefit. That means you could potentially increase crop yields just by playing the right sounds.

Hearing isn’t the only unusual thing mycelium can do. They can also eat things that can’t normally be eaten, like radiation. We covered how a mycorrhizal network can potentially benefit both fungus and tree life by sharing nutrients back and forth. This is because there are certain nutrients that fungi don’t make on their own, or don’t make nearly as efficiently as other plants do.

The same theory applies to fungi when it comes to radiation. Certain kinds of fungus, in places like Chernobyl, have adapted to feed on radiation. Just like a tree converts sunlight into energy through photosynthesis, or you turn your tacos and pizza into energy by consuming the calories via digestion and metabolism, these fungi absorb gamma radiation and turn it into energy.

Research into using radio‑adaptive fungus to not only clean up radioactive zones but also detect secret nuclear facilities has been proposed.

Mushrooms have long been known for radiation resistance. In one study, mice that were fed black mushrooms exhibited higher than normal protection from external radiation. So eating mushrooms, dark ones that contain melanin, could literally protect soldiers and others exposed to dangerous radiation. Something to think about the next time you’re worried about some X‑rays.

4. Fungal Brains

We said a little earlier that a mycelial network forms more connections than a human brain. That’s not the only way fungus has been likened to a human mind. Research has shown that these networks have a sort of memory and also decision‑making abilities. This information seems almost unbelievable at first, but we have plenty of evidence that other organisms like octopus and crows possess remarkable intelligence, so why not an organism that is so vastly complex?

In experiments, the hyphae in a network have demonstrated spatial awareness. They will alter how they develop based on interactions with other organisms. Fungus has been shown to remember stressful experiences for up to 12 hours and avoid where and how it happened.

If a wood block is placed in the soil with mycelium as bait, a source of nutrients, and then moved, the remaining mycelium will continue to grow to where the block used to be, indicating that the larger organism remembers where it once was.

When networks are allowed to grow, they do so in ways that preserve resources and limit stress. Their growth patterns indicate that the whole network is connected and communicating so that the entire organism “understands” what is best for it. Or, in other words, it functions like neurons in a brain.

The functioning of these hyphae has been measured with microelectrodes and has shown that membrane polarization and depolarization occur across the hyphal membranes, and it resembles nerve impulses in animals. The function in fungus, however, is still unknown, but it may even be related to language.

Research into these electrical impulses shows that at least some forms of fungus produce signals that resemble a simple language. The signals increase when the network discovers a food source, for instance.

Recordings of the electrical impulses were searched for patterns, and it was discovered that similar spikes occurred in similar situations, or trains of activity. In fact, the team was able to discern about 50 words throughout these activity trains that were, on average, about 5.97 letters long. English averages about 4.8 letters per word.

The researcher behind the observations was quick to point out that this may be a simple way for the network to identify food sources and things that it wants to stay away from. And it’s just as likely this is not a form of communication at all. However, whatever the impulses are for, they are not generated randomly, so they do serve a purpose.

The mycorrhizal network allows linked organisms to share warnings among themselves. Tomato plants infected with a disease called early blight were able to transmit this information to uninfected plants nearby, which allowed them to start producing a defensive enzyme to ward off the disease. Stress signals were transmitted through the mycelium, and the healthy plants received and reacted to them.

Biology professor Nicholas Money proposed the idea that fungal networks possess what he called a “minimal selfhood.” They don’t have intelligence at the level of a human mind by any means. The network is not nearly as complex as a brain, but it is complex nonetheless, and fungus shows a sort of rudimentary consciousness defined by its ability to maintain itself and reproduce.

Whatever information that a mycelial network can convey, there’s definitely something happening, and it’s not just with the fungus. It’s with the other organisms that they connect.

5. What Are Mycelial Networks?

A mycelial network is a fungus; it can get very big, and it’s underground, eating trees. What else? The mycelium are fine, hair‑like threads that weave together underground. They look almost like a loose‑knit blanket weave in some species, depending on how densely they are packed together. But it’s not that easy to see it all. Some of these individual “roots” are thinner than a human hair.

Known as hyphae, these thin filaments can be just two micrometers in diameter, while a hair is a positively girthy 17 micrometers. As they branch out in all directions, they make more connections than a human brain.

Over 100 miles of mycelium can be packed into just over 2 pounds of soil. This is how they form a mycelial network, which is the vast structure of threads, or even a mycorrhizal network, which is slightly different.

A mycorrhizal network is a mycelial network that is symbiotic between fungi and other plants, like trees. Unlike our big friend in Oregon, which eats the roots and kills the trees, fungi that form a mycorrhizal network help the trees they connect with.

How does all this work? The fungus can draw nutrients from dead matter and soil since fungus can feed on almost anything. It will transfer these nutrients to the tree roots and, in exchange, get some of the tree’s photosynthate, the energy it derives from the sun, which is something the fungus can’t do on its own. As much as 30% of the sugars produced by photosynthesis will go to the fungus in this way.

In human terms, imagine a tree as your friend who loves tacos, and you as a fungus who loves pizza. You both have a good meal alone on Friday night, but if you hang out, you both get to have tacos and pizza, and isn’t that better for everyone? The answer is yes.

Water, nitrogen, carbon, and all sorts of other minerals that are, admittedly, less delicious than tacos and pizza, are shared between the organisms to the benefit of all. It has been theorized that the fungus is mostly rewarded with carbon from the trees, and the trees get phosphorus and other minerals.

What makes it a network is that the mycelium doesn’t just latch on to one tree. As with the giant in the forest in Oregon, these can spread to many trees, connecting each one to allow them to share nutrients and keep a whole grove, a whole forest, thriving. This is especially helpful when some trees, like saplings, are hidden from sunlight or located in a place where water is more scarce.

In cities the majority of space is off‑limits. Parks and streets may account for up to half the total area, but when you factor in the vertical axis—the floors inside buildings (many of them empty)—you get a different picture. And that’s just the space that we know about. Often there’s a lot more underground.

10 Mumbai’s Imperial Underworld

When an occupying force takes over your country, it tends to cut you out of the loop. Hence, whenever Indian construction workers find structures under cities once controlled by the British, they don’t know what they were built for. The vault beneath Kolkata’s National Library, for instance, might have been anything from a treasury to a torture chamber—and, as it eventually turned out, just part of the building’s foundations.

Mumbai has a veritable underworld of abandoned imperial structures, from the 13‑room bunker under Raj Bhavan (the seat of city government) to the kilometer‑long tunnel under the old General Post Office.

Another mystery was unearthed as recently as 2022: a 200‑meter tunnel under Mumbai’s JJ Hospital, a building whose foundations were laid by the British governor. Appearing on no maps, it was only discovered in a water‑leak survey. And it was blocked at one end so it wasn’t clear where it once led. While it’s thought to have been to a neighboring hospital, it remains something of a mystery for now—as does the number of underground structures that remain to be found in Mumbai.

9 LA’s Prohibition Partyways

While the rest of America endured its first War on Drugs—the doomed‑to‑fail prohibition of alcohol—the mayor of LA kept the hooch flowing through a network of underground service tunnels. These were also the routes by which the flappers and dapper gents of the city’s roaring party scene got from one bar to the next without hassle. Originally built as service tunnels, and for a subway to ease traffic on the surface, they ran for more than 17 kilometers connecting basements converted to speakeasies.

One such bar was the King Eddy Saloon. Established almost 20 years before Prohibition, it moved underground to survive—transforming its above‑ground premises into a piano store. Others include the Edison, in the basement of the city’s first privately owned power plant, and Cole’s, under the Pacific Electric building. Patrons of all these establishments, armed with a password, stumbled around wasted, completely unseen by police and paparazzi.

Despite their historic significance, the passages and basements are now closed to the public and even largely unmapped. Many are flooded and crumbling. Just like in the old days, however, those in the know can find their way in—as evidenced by the tunnels’ graffiti. According to Atlas Obscura, there’s an “easy‑to‑miss elevator” on Temple Street. And there’s also, apparently, an entrance off the subway from Downtown to Hollywood.

8 Havana’s Secret Chambers

In the early 1990s, the Cuban government was reported to have secretly built more than 33 kilometers of tunnels under Havana. These were to serve as bomb shelters amid escalating threats of invasion by the United States.

Known as the Popular Tunnels, they were manually dug by hundreds of laborers and their entrances carefully hidden. But these were just the latest of a long tradition of tunneling under Cuba. All the way back in 1929, the New York Times reported on the discovery of five secret chambers under Havana’s City Hall.

7 Tokyo’s Hidden Network

From rivers and forgotten canals to the world’s largest sewer system, there’s plenty below Tokyo that we know about. But there may be a lot more. When journalist Shun Akiba compared an old map to a new one, he found differences suggesting not only unknown tunnels but an effort to cover them up. Whereas the new map showed subway tunnels crossing in Nagata‑cho, close to the National Diet building (the seat of government), the old map showed them as parallel. Shun also found evidence of an underground complex between the National Diet and the prime minister’s residence. He also remarked on the mysterious tunnels leading off the Ginza Line.

Official enquiries got him nowhere, he said, lips were “zipped tight” despite his respectable professional background as a war correspondent for Asahi TV. From what he’s seen, Shun believes there must be close to 2,000 km of tunnels beneath the city—eight times the stated 250 km. And many of them (the Namboku, Hanzomon, and O‑Edo lines, for instance) were built long before their conversion for trains. That the Chiyoda line platform at Kokkai‑gijidomae, the National Diet station, is the deepest in Tokyo, suggests it was built as a bomb shelter. Yet old blueprints show another level even deeper. There’s also the mystery of the Yurakucho line, which, with its high ceilings and military facilities on route, is rumored to be a secret road used by the military. Although the network dates back to World War Two and the Cold War era, the continued silence from officials suggests they may still be in use.

6 Washington’s Whack‑a‑Mole Hidey‑Holes

The two main parties of the military‑industrial regime based out of Washington have plenty in common, but one thing stands out: they’re both afraid of the public. Hence their underground tunnels to get from one building to another—tunnels they’re advised to make use of. Some of these famously served as evacuation routes during the 2021 Capitol siege, but they are in fact used every day just to avoid going outside.

According to The Drive, there’s “a labyrinth of at least 19 underground passages on Capitol Hill”, not only for people but vehicles as well. The oldest date back to the 1800s, when they were built for water and ventilation, as well as to transport books by electrical conveyor belt between the Capitol and Library of Congress. When the Russell building was finished in the early 1900s, it came complete with a subway car system in a tunnel so fortified that it was, many years later, designated as a fallout shelter. As other buildings followed, the tunnel network grew. And nowadays the Cannon Tunnel, between the Cannon building and the Capitol, is more like an underground town with “a shoe repair store, post office, credit union, and cafeteria.”

Among the most recent major works was a 54,000‑square‑meter expansion of the Capitol building’s underground complex. This added three underground stories to the existing network with links to nearby offices and a 305‑meter tunnel to the northwest, officially built for screening garbage trucks for explosives. That was in the 2000s, amid growing secrecy regarding Washington’s underworld—not to mention the tunnels and bunkers that lie deep under the White House.

5 Moscow’s Many Secrets

The largest of Europe’s old fortresses, the Kremlin sits atop a labyrinth of secret passageways. There’s the haunted Neglinnaya river tunnel, for example, the Syani stone mines where the city sourced limestone for construction, and, although it’s yet to be found, the library of Ivan the Terrible. Excavations for the latter have all turned up nothing but tunnels: “endless tunnels, buried, stoned in, heading in unknown directions”. While the search was called off, however—in part because of damage to foundations—the library’s still thought to be down there, along with its priceless collection.

What has been found are the dungeons under two of the Kremlin’s towers, in one of which Ivan the Terrible imprisoned Prince Andrei Khovansky. Those condemned to torture were kept gagged and chained to the wall, allowed to speak only when addressed by their captors. The nearby dungeons of the Cathedral of the Archangel kept prisoners of the church, people who owed it money, on painful posts known as “penitence chairs”. Just next door are the cathedral’s stone treasuries, built to withstand both fires and theft.

Much more recently constructed was the Metro‑2, a parallel subway system built, in secret, around the same time as the main one. Intended to evacuate the government, it runs as deep as 250 meters in places. And not much is known about it, either, except that it does exist; Moscow’s first post‑Soviet mayor confirmed that in 2006.

4 New York’s Abandoned Subways

There are numerous disused rail tunnels under New York City. Track 61 beneath the Waldorf Astoria is among the most storied, having once carried presidents and generals like Roosevelt and MacArthur. In 2003, it was even considered as an escape route for George Bush. It has also hosted a fashion show and an Andy Warhol event. Other subways were constructed for the mail, such as the Farley‑Morgan Postal Tunnel under 9th Avenue. Although it’s sealed off now, it was briefly used in 2004 to sneak guests between venues for the Republican National Convention.

The Atlantic Avenue Tunnel under Brooklyn, meanwhile, has been abandoned since 1861—less than 20 years after it was built in 1844. It’s the oldest subway in the world and was only briefly reopened in 1918 to look for Germans.

But there’s a lot more under New York besides subways. One of the most interesting and unique tunnels is the 66‑kilometer underground aqueduct between Bryant Park and the Croton River in Westchester. Disused since the 1950s, this “perfectly preserved” tunnel—the 1842 Croton Aqueduct—once carried millions of gallons of water to the city. It was all stored at the Distributing Reservoir in Bryant Park, a vast, 16,000‑square‑meter structure resembling an ancient Egyptian temple. It was actually thanks to this place, the solution to Manhattan’s disgusting sanitation problems, that the city is still there today.

3 Rome’s Ancient Quarries

So extensive are the ancient tunnels and quarries under Rome, dating back to the founding of the city, that it’s common for sinkholes to form and for buildings on the surface to collapse. It was only in 2013 that geologists mapped the network, amid an increasing number of such incidents. There were 44 collapses in 2011, followed by 77 in 2012, and 83 by December 2013. Residents have usually patched up the damage themselves using big plastic bags of cement.

The original Ancient Roman tunnelers actually tried to guard against this happening (in their own day, at least) by keeping the passageways narrow. This ensured the surface was still largely supported. Over time, however, the exposed rock has weathered. Not only that but later generations have widened the original tunnels and kept building more.

Although they’re not open to the public, they’ve been used by Romans down the ages as catacombs, sewers, and mushroom farms, as well as shelters in the Second World War.

2 London’s Tunnels of Intrigue

With its dungeons, crypts, and catacombs, 13 underground rivers, and plague pits from the mid‑1300s, the history of London lies just below the surface. More recently, however, officials confirmed what urban explorers have known for decades: the existence of a sprawling network of underground tunnels connecting government buildings with secret chambers. According to the Land Registry in 2017, most of them were built by the Post Office, British Telecom, and the Ministry of Defence.

One of the more interesting parts of the network, the Postmaster General’s tunnel, runs from the East End of London to what used to be the War Office at 57 Whitehall (now an overpriced hotel). At various points along the way, elevator shafts connect it to government departments and telephone exchanges. Deep under High Holborn Street, not far from Whitehall, one such exchange was built as a government bomb shelter, complete with a restaurant, games rooms, and two bars (one for tea and one for booze).

The tunnels have, officially, been out of use since the Cold War era, but they were never opened up to the public. While those who’ve managed to sneak down there do say it’s like a time capsule, untouched in decades, they’ve only seen parts. Access to the deeper levels is suspiciously bricked off, the lights are kept on, and trespassers are disproportionately punished.

1 Beijing’s Underground City

Built to hold 40% of citizens in the event of a war with Russia, Beijing’s dixia cheng (“underground city”) covers a remarkable 85 square kilometers—all hand‑dug by citizens during the Cold War. It’s also known as the “underground Great Wall of China”, for its massive scale. But you’re not allowed to see it.

The official guided tour takes in only a small, looping, and commercialized fraction of the whole. The rest of the corridors, tunnels and bunkers are said to be inhabited by up to one million homeless—the so‑called Rat Tribe (who presumably stand to inherit the Earth). But that sounds too good to be true. While some of dixia cheng has been converted to low‑cost, sub‑standard apartments, it’s hard to imagine the CCP leaving all of it to poor people and tramps when there are hundreds of more selfish uses. With 90 entrances across the city, for example, its potential for “disappearing” citizens is obvious.

In any case, whatever’s really down there, it was built for long‑term habitation, with storage for grain and space for mushroom farming, as well as restaurants, barber shops, a cinema, classrooms and anything else to help persuade citizens that things were still normal.