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Introduction: The Fungal Puppet Master
The idea of an infection that could turn humans into mind-controlled monsters is something that has fascinated our culture for almost 100 years, following the publication of ‘The Magic Island’ the worlds first zombies novel. Since then zombies have exploded in popularity with hit TV shows such as ‘The Walking Dead’ and blockbuster movies like ‘World War Z’. Although zombies are strictly written about as science fiction, across the animal kingdom, the terrifying reality of zombies is a fact.
Ophiocordyceps Unilateralis, or cordyceps for short, is a species of fungus. Contrary to common belief that fungi are a type of plant, they are a completely different type of life altogether. Just as animals and plants are totally separate from one another, so too are fungi. Unlike plants the don’t photosynthesise, so instead of getting their energy from the sun, they have to feed on plants, or as we will come to see, animals – dead or alive. When a living organism feeds off of another living thing, this is known as a parasitic infection.
“[Cordyceps] is one of the most extraordinary examples of parasitism in nature, blending the line between life and death.”
Dr. David Hughes
Parasitic infections are common across the animal kingdom. Everything from fleas on a cat or a dog to tapeworms that can grow to 30ft long, and attach themselves inside the stomachs of animals, and even humans. In most cases parasitic infections are very unlikely to kill the host that they infect, as they rely on the host to survive in order to keep receiving a portion of their nutrients, and will at most cause irritation to the host. However, Cordyceps is unique in this scenario, as following infection, it causes far more than irritation, the fungus manages to slowly take over the host’s body. Cordyceps takes control of every muscle and nerve of its victims, spare the brain, leaving the host to watch in horror, as Cordyceps climbs into the drivers seat. Once the puppeteering is done, Cordyceps kills its host, and feasts on its worn out play thing.
What is Ophiocordyceps? The Fungus Behind Insect Mind Control
Cordyceps was discovered in 1859 by the British naturalist Alfred Russel Wallace, in Sulawesi, Indonesia. Unfortunately following the collection of his specimens, Wallace’s ship sank on its return to London, destroying the specimens entirely, delaying our understanding of the fungus for several years. Since their initial discovery the Ophiocordyceps genus (the wider family of the Ophiocordyceps Unilateralis fungus) is known to have over 200 species within it. Incredibly almost all of these species closely related to Cordyceps, infects a different insect or arthropod in a very similar manner to Ophiocordyceps Unilateralis.
Ophiocordyceps unilateralis primarily infects ants of the Camponotini tribe – the most commonly known of which are carpenter ants. These ants, as well as the Cordyceps fungus, are found primarily in subtropical forests, in regions such as South America in Brazil, Australia, Asia in Thailand, and several regions across Africa. Many members of the Cordyceps genus have adapted to survive in different climates, being able to affect hosts of different species all around the globe.
How the Fungus Infects its Hosts: The Zombie Transformation
The idea of a fungus controlling the behaviour of arguably more concept organisms, is what has led to such scientific intrigue revolving around this utterly fascinating orgaminsm. The real point of fascination for current science, is the way in which the fungus alters the nervus system of its victims, and forces them to act in ways the solely benefit the fungus. This process is a continuous lifecycle for Cordyceps, infection, to mind control, to muder, to rebirth. This is made even more valuable to science, as Cordyceps, throughout its life-cycle, produces many antibiotic compounds, to protect itself from bacteria kicking it out of its new host.
Infection Initiation: The Beginning of the End
Cordyceps begins its life-cycle as microscopic spores, being carried around on wind currents and dispersing itself around the sub-tropical rain forests which it calls home. The spores have highly specialised outer capsules, which, when an ant comes into contact with a cordyceps spore enable them to stick to the surface of the ant’s exoskeleton. Once attached, germination of the spores begins, and long thread-like filaments known as hyphae begin to branch out from the spore, penetrating the ant’s exoskeleton and burrowing, like roots into the body cavity. By releasing specialised compounds, the hyphae manage to evade destruction by the ant’s immune system, and the fungus begins to grow.
Growth of the Fungus: The Art of Mind Control
Inside the ant the fungal cells, now growing, begin to spread throughout the body of the ants, consuming nutrients from each of the ant’s tissues, in order to grow further and continue its spread. Once the fungus reaches the brain of the ant, instead of taking control of it, it leaves the brain alone. Whilst this may seem like a blessing at first glance, it is where the true nightmare of cordyceps begins. The fungus instead attaches itself to the central nervous system of the ant – each and every nerve and muscle outside of the brain, setting itself up for the perfect puppet show. Without infection of the brain, it can be assumed that the ant effectively becomes a passenger in watching its own life end.
Around 3 weeks after the initial infection the ant begins to show peculiar erratic movements, convulsing and contracting, unable to control its own body any longer. Now infected, the ant will abandon its colony, something that is otherwise almost unheard of for ants, as without their colony, they are vulnerable, and leaving is ultimately a death sentence. The ant then goes into a ‘wandering phase’, where the fungus begins to learn to control its host, causing the ant to walk aimlessly around the forest floor, regularly convulsing and collapsing to the ground. After walking for several hours or even days, the ant’s body begins to climb.
Death Grip: The Final Stage of Infection
The infected ant finds a large piece of living vegetation and it begins to climb. The ant will climb to an incredibly specific height, normally 25 centimeters above the forest floor. This height is optimal for the growth of the fungus and spread of the fungal spores. There the ant will find the underside of a leaf and clamp its mandible to a vein of the leaf. From there the ant will go into lock-jaw and it will stay in this position, clamped to the underside of a leaf, for the remainder of its life. Within the following few days, the ant will die, and the fungus, feasting on its new meal, will grow and enormous fruit, out of the ant’s head. This fruit then spreads the spores throughout the air, starting the cycle all over again.
The Science Behind Fungal Mind Control: How Does it Work?
Unlike the process of ‘zombificaion’ in pop-culture, instead on infecting he brain, the Cordyceps establishes a widespread network of fungal cells, that integrate with the ant’s muscle fibres. This network effectively hijacks the ant’s body, turning its muscles into a puppet, leaving the brain untouched.
This puppeteering act is conducted primarily by the series of neuro-active compounds that are released by the Cordyceps fungus into the ant’s nerves and muscle fibres. Muscles and neurons around the ant’s body are ordinarily controlled by several key chemicals, including serotonin and dopamine, for everything from muscle movement to mating behaviour. The chemicals released by Cordyceps interrupts the delicate balance of these chemicals, and causes the ant’s brain to lose control submitting the body to Cordyceps. At the same time, the fungus continually releases manipulative proteins into the ants nervous system that stop the host’s immune system and change its behaviour with truly chilling precision and accuracy.
The survival and reproduction or Cordyceps depends on a highly specific timing schedule. Kill the ant too slowly, and it may be eaten and destroyed by a bird or larger animal, kill it too quickly and it wont be able to manipulate the ant to best spread the fungal spores. To achieve this, the fungus meticulously manages its spread within the host. In the initial infection, Cordyceps will only consume non-essential tissues to the ant like fat and a small amount of hemolymph (the ant equivalent of blood). It also begins to enter into the ant’s muscles, very gradually, to avoid harming any vital organs of the ant. The final phase of growth will only happen when the ant has locked its jaw, high in the sky, in its final resting place. At this point the fungus ramps up the feast on the ant, and can kill the ant within a few hours, degrading the host’s tissues with oxidants, essentially dissolving the ants innards for an easy meal.
Supporting Research: The Study of Zombies
Recent research has shed light on how Ophiocordyceps takes control of its host. In 2018, scientists mapped the fungus’s genome and pinpointed specific genes involved in host manipulation. Throughout the infection process, the fungus adjusts its gene activity to precisely control the ant’s behavior at different stages. Interestingly, some of the proteins produced by the fungus are similar to those used by animals to regulate their nervous systems, suggesting the fungus evolved a similar mechanism to control its host without directly affecting its brain.
A 2019 study found that Cordyceps can control an ant’s movements without invading its brain, suggesting the ant may still be aware of what’s happening but is powerless to resist the fungus’s control. Instead of turning the ant into a “zombie,” the fungus controls from outside the brain, leaving the ant’s mind intact while dictating its actions.
In 2017, scientists used electron microscopy to observe fungal cells wrapping around the ant’s muscle fibers, acting like a “second nervous system.” This fungal network allows the parasite to control the ant’s physical actions without directly interfering with its mental processes. As a result, the ant isn’t truly mindless but is controlled externally by the fungus. This intricate system highlights the remarkable adaptations that Cordyceps has developed to ensure its survival.
The Evolutionary Arms Race: How Insects Fight Back
Whilst the ants seem to be in a losing battle against Cordyceps, evolution, as it always does is putting up a fight, keeping Cordyceps and ants in a biological war, pushing and pulling the balance of power. Certain ant species that frequently encounter Ophiocordyceps infections have developed genetic adaptations to resist fungal invasion. Some mutations strengthen the exoskeleton, making it harder for fungal spores to penetrate, while others boost immune system responses, helping ants fight off the fungus before it takes control.
As well as individual adaptations, there are even wider social responses to prevent Cordyceps infection. Ants in fungus-prone areas instinctively avoid contaminated sites and change their foraging routes when spores are detected. If infection rates rise, colonies may relocate to a safer location. Grooming is also a critical first line of defense. Ants meticulously clean themselves and each other, removing spores before they can penetrate the exoskeleton. Some colonies even have specialized worker ants dedicated to intensive cleaning to protect the entire group. Some ants modify nest entrances and tunnels to limit contamination, blocking infected ants from re-entering. Other insects, like termites and bees, can raise their colony’s temperature to inhibit fungal growth. Infected ants sometimes engage in altruistic behavior, leaving the colony or isolating themselves to prevent the spread of spores. Some even exhibit an immune defense called encapsulation, where immune cells surround and neutralize fungal spores, much like how human immune systems isolate foreign invaders.
Can Mind-Controlling Fungi Infect Humans
The idea of parasitic fungi turning humans into zombies has gained mainstream attention, thanks to pop culture phenomena like The Last of Us. While the concept makes for an exciting (and terrifying) story, how realistic is it? Could a fungus like Ophiocordyceps ever evolve to infect mammals, including humans? Scientists say it’s highly unlikely—but not entirely impossible.
Although the ‘Last of Us’ scenario makes for brilliant television, at the current time, it unfortunately is just science fiction. Fortunately for the human race there are several barriers that prevent us becoming infected by cordyceps. The human body sits at 37°C, and the Cordyceps can only survive at a maximum of 30°C, so when it enters the human body, it effectively gets cooked, killing it before it can cause any damage. The nervous system of humans is also far more complex than that of ants, and the currently simple mechanisms of chemical release in ants to control their behaviour and movements would be currently be ineffective in humans. And thankfully, whilst fungus is a growing threat to humans, due to many fungal adaptations to global warming, allowing more and more fungal species to infect humans, there have still yet to be any reports of Cordyceps infections in animals.
Could a Mutation Make Human Zombification Possible?
While Ophiocordyceps poses no threat to us, several other fungi can be dangerous or even deadly. Candida auris causes multidrug-resistant bloodstream infections, Cryptococcus neoformans can invade the brain and lead to meningitis, and Histoplasma capsulatum causes lung infections when humans inhale spores. The greatest fungal risks come from opportunistic infections in immunocompromised individuals like those with HIV or AIDS.
“Fungi are the greatest threat that no one is thinking about.”
Dr. Arturo Casadevall
Some scientists warn that climate change could increase fungal threats to humans. As global temperatures rise, fungi may evolve greater heat resistance, potentially enabling more species to survive in human bodies. While this doesn’t mean Ophiocordyceps will turn humans into zombies, it may lead to more emerging fungal diseases. The increase in potential fungal infections and a severe lack of anti-fungal medications currently in existence mean fungus pose a serious future threat to global health.
Conclusion: Nature’s Strangest Parasite
The story of Ophiocordyceps unilateralis reveals just how bizarre and ingenious nature can be. This mind-controlling fungus has evolved an intricate system to manipulate its insect hosts, creating a real-world “zombie” phenomenon. Through precise control over the ant’s nervous system and behavior, Ophiocordyceps ensures its survival and reproduction – a chilling yet fascinating example of nature’s complexity.
Despite its terrifying capabilities in ants, the fungus poses no immediate threat to humans. The barriers of heat sensitivity, our complex immune system, and the intricacies of human neurology make it highly unlikely that Ophiocordyceps could ever adapt to infect us. However, the rise in fungal threats to humans, driven in part by climate change, is a growing concern in the medical community. Opportunistic fungal infections like Candida auris and Cryptococcus neoformans highlight the need for continued research and vigilance as fungi evolve and adapt to new environmental pressures.
Ultimately, while the zombie apocalypse remains a work of fiction, the real-world story of Ophiocordyceps offers a glimpse into the incredible diversity of life on Earth. It serves as a reminder of the ongoing evolutionary arms race between hosts and pathogens—one of nature’s most enduring battles.
References
- Will I. Genetic Underpinnings of Host Manipulation by Ophiocordyceps as Revealed by Comparative Transcriptomics (2020)
- Maridel A. Three-dimensional visualization and a deep-learning model reveal complex fungal parasite networks in behaviorally manipulated ants (2017)
