David Hughes leans back in his office in a standard-issue professorship chair as Penn State students in a plaza behind him shuffle toward classes. Between us on his desk—on either side of a paper cup of black coffee—are two trays of dead ants stuck through with pins. Some cling to leaves, others curl up around sticks, frozen in their tiny death postures like the now-fossilized humans who couldn’t escape Pompeii. All, though, have strange structures erupting out of their corpses.
This is how ordinary ants become zombies. Walking dead. Pawns of an insidious and spectacularly clever fungus.
Hughes pivots his monitor to show me a microscope photo of an infected ant’s muscle. More specifically, an ultra-thin slice of an ant muscle, so the blobs we’re seeing are cross-sections of fibers. Between these blobs, though, are tinier blobs—fungal strings that have grown through the muscle fibers, prying them apart.
Photograph slice after slice of an ant muscle like this, use AI to detect the bits of fungus and paint them green, and stack the photographs once more to make a 3-D model, and you can start to grasp the destruction the fiend has wrought. What Hughes has imaged is a muscle overwhelmed by fungus, insidious strands of green growing like grass between the fibers.
A fungus called Ophiocordyceps—to be referred to henceforth as Ophio for the sake of brevity and to cut down on misspellings—infiltrates and hijacks the ant’s muscles, but doesn’t touch its brain. “It’s basically just punching holes in the muscle,” Hughes says, pointing to said muscle. “So this is really strong atrophy, the same kind of stuff that would happen if you broke your spine.”
The fungus severs the nerves in the muscle, cutting off communication with the brain. Essentially, crippling the nervous system. And that wouldn’t seem to make a lick of sense, because up until the end, the fungus isn’t paralyzing the ant, but instead assuming precise control over its faculties.
“If I had to guess, and this is completely speculative,” Hughes says casually, “I think the fungus is forming a nervous system.”
This tale begins with the humble Ophio fungal spore living in a rain forest. Once it hits the ground, it sprouts a secondary spore that grows vertically, tipped with a bit that catches on an ant’s exoskeleton. “And these have backward-facing spines in some species,” Hughes adds. “So they just attach”—emphatic clap—“like a limpet mine. And then they literally blow a hole and eat through the cuticle at the same time.” That’s thanks to enzymes that break down the ant’s armor, plus the spore builds up pressure to equal that in the tire of a 747.
Kaboom. The fungus is in.
And what a wonderland it has found, for the ant is not just its vehicle, but an energy-rich battery. An insect is not built like us—it has an open circulatory system, so things are more or less sloshing around in the absence of a network of arteries and veins. It’s not hard, then, for the fungus to get about. As it multiplies, it soaks up more and more of its host’s nutrients.
Exploratory bits of Ophio, known as hyphae, branch out to find ever more food, growing as a network throughout the body. Fungal cells infiltrate the muscles, breaking the fibers apart. All the while, the fungal colony is talking, forming so-called anastomosis tubes—think of them like pneumatic tubes, only without the vacuum.
“This fungus has joined together in a group and they’re communicating and they’re exchanging things, that’s what anastomosis is,” Hughes says. “The question is what they’re exchanging and what they’re doing. We don’t know.” It may well be food, the exploratory bits ferrying nutrients throughout the network.
In any case, it continues to multiply, spreading farther and farther, eventually reaching the brain, where it . . . stops. The Ophio fungus, for all its powers of mind-control, never invades the ant’s brain. Instead, it grows around the thing as a sheath. After all, the fungus wouldn’t want to risk crippling its vehicle.
After three weeks of growth, the fungus will make up perhaps half the insect’s weight and is now ready to flip the switch and essentially take over the ant’s body. Up to now, the ant has acted normally—no stumbling, no aggression—nothing that would alert its colony to an intruder. The fungus within has been able to diversify into different tasks. Some bits mine nutrients, some attack muscles, and some surround the brain, ready to release a chemical bomb.
When that bomb drops, the Ophio fungus induces the ant to do the unthinkable: not only leave its beloved colony, but to sabotage it. Away from the watchful eyes of its comrades, the ant now begins staggering. It might convulse its way up a tree trunk, tripping along a branch and onto a leaf, sinking its mandibles into the vein. The fungus having taken control of the mouth muscles, the ant assumes a death grip. Six hours later, the victim perishes, and the fungus consumes what little remains of its insides.
Critically, the fungus has steered the ant 10 inches off the ground, where the temperature and humidity are best for the astonishing growth it’s about to undertake. The Ophio has to work quickly, for the rainforest is teeming with all manner of other fungi (perhaps 40,000 spores of various other species on a single leaf) and bacteria that would happily consume what remains of the ant.
But the parasite is prepared: Cross-section an ant at this point and you’ll find that among the white hyphae that have replaced the ant’s insides is a band of orange. This is packed with carbohydrates and probably feeds the maniacal growth of the fungal stalk that erupts out the back of the ant’s head. Hyphae also pour out of the ant’s mouth, further securing the mandibles to the leaf, and proliferate as a sort of fuzz on the ant’s cuticle, protecting the prize from invaders. Everything thus in order, the Ophio stalk matures and begins releasing spores, which descend onto the hapless ants marching below.
To fully comprehend the majesty of fungal zombification, we have to first understand the majesty of the ant society. Ruling the colony is a queen. The vast majority of the young she produces are females—the workers who dedicate their lives to the queen and each other. Cooperation drives the whole operation, the ants foraging and sharing resources and fighting other colonies to protect their territory. Thus the colony works as a kind of super-organism, thousands of individuals banding together like cells to create one body in pursuit of reproduction on a grander scale.
Problem is, each cell is an entry point for parasites with cruel intentions, so our super-organism needs an immune system of some kind. What the ants have landed on is called social immunity: Each individual acts as an immune cell to detect and eliminate intruders. So if someone is acting oddly—say, staggering around—that’s an indication that she’s host to something nasty that could destroy the colony if not quarantined. A worker will pick her up, drag her outside the colony, and dump her in a graveyard of other diseased ants.
This system presents a problem for Ophio. It has to grow within an ant, yet not alter its host’s sociality, a tricky task when it’s wrenching apart muscle fibers. So somehow the fungus is able to time it such that the ant only begins stumbling once she’s on her way out of the colony and up the tree. Not only that, but Ophio has to avoid the colony’s immune cells literally sniffing it out, for ants use pheromones—or chemical cues—to identify each other and communicate things like the location of food.
So to get anywhere at all, Ophio has evolved to fool the super-organism that is an ant colony, and its solution is body-snatching. If it made the ant start acting in any way funny, it’d be evicted. If it made the ant smell weird, it’d be evicted. And if it dispatched the ant within the colony and started growing a stalk, it’d be evicted.
Maybe the key was the muscles. Maybe long ago Ophio started out consuming those tissues and eventually figured out how to manipulate them instead, prying the fibers apart, crippling them. “What happens with rigor mortis is the calcium stops flowing in and out of your muscle cells,” Hughes says. “And I think what they’ve done is induce a functional rigor mortis in a living ant.” It’s the real-life living dead.
This means the fungus doesn’t need to dig its way into the brain, but that’s not to say Ophio isn’t in some way affecting the ant’s mind. Indeed, looking at the fungus’ evolutionary tree could give us some insight into what’s happening here. Namely, Ophio is closely related to a fungus called ergot, which in 1938 a Swiss scientist by the name of Albert Hofmann synthesized into lysergic acid diethylamide. But you probably know it as LSD.
Now, we can’t begin to know if an Ophio-infected ant can hallucinate. But if you were to open up one’s brain and take a tissue sample, you’d find 55 times the normal amount of ergot-like alkaloids, which resemble neurotransmitters. So the Ophio cells that surround the brain are probably dosing the ant—big time.
But again, the fungus is striking a balance here: It has to drive its host mad yet not mad enough that the colony raises the alarm. And the bits around the brain releasing the chemicals have to communicate with the rest of the fungal network throughout the ant without sending the whole system into disarray. Remember some of the fungus soaks up nutrients and other hyphae pull the strings in the muscles. “It makes a lot of sense,” Hughes says. “If you’re in the back of the bus, you don’t need to produce the chemicals that affect the driver. You’re just waiting until the driver is manipulated.”
One particular strain of Ophio, which calls the United States home, goes about things even more cleverly. And that beggars common sense, Ophio moving so far north from the tropics, where in the winter fungus-nurturing conditions fade away and ant-bearing leaves shrivel and fall from trees. Yet here in the forests of the US, the zombie ants perish in vast killing fields.
In South Carolina, where leaves fall from trees in the winter, the zombie ants aren’t biting into the veins of leaves and perishing—they bite onto twigs and perish. By ordering its ant to take hold of a twig, this variety of Ophio ensures it maintains its perch no matter the time of year. That’s particularly important considering the lower temperatures in a temperate clime retard the growth of the fungus. The fungus’ growth slows in winter, and it sometimes even ices up and goes into a kind of stasis, yet revives in the spring and continues development, all so it can one day ruin the lives of other ants.
Adapted from PLIGHT OF THE LIVING DEAD by Matt Simon. Copyright © 2018 by Matthew Simon. Published by arrangement with Penguin Books, an imprint of Penguin Publishing Group, a division of Penguin Random House LLC.