How a fungus turns ants into biological puppets

HostI was sitting out in the garden earlier today, watching a line of ants crawl across the patio, and I started thinking about zombies. We always see them in movies as these mindless things that have lost their spark, but I was reading about a type of fungus that takes over ants in a way that's much more unsettling. It's almost like the ant is still awake inside while its body gets hijacked.

GuestThat's the part that really sticks with you. When this specific fungus lands on a carpenter ant, it's not looking to turn the brain off. It actually leaves the brain alone for most of the process. We used to think it was just a simple brain parasite, but it turns out to be way more clever and a lot more physical. It's less like a virus and more like a hostile takeover of the ant's body while the ant is still at the controls, but someone else is suddenly steering the ship.

HostBut an ant has that hard outer shell. It's basically like a suit of armor. How does a tiny spore even get past that?

GuestYou would think that shell would protect them, but the fungus has a two-part plan to get inside. First, the tiny spore lands on the ant and uses a lot of physical pressure to push against the shell. At the same time, it lets out a mix of special chemicals that act like a slow-motion acid to melt a hole right through that armor. Once it's through, it gets into the ant's blood and starts making copies of itself. It goes from these tiny single cells into a massive, tangled web of living threads. At this point, the ant looks totally normal to all its friends in the colony, but on the inside, the fungus is slowly eating the organs it doesn't need to stay alive, using them as fuel for the next step.

HostI'm sorry, I have to stop you there because you said it doesn't use the brain. If the fungus isn't in the brain, how's it making the ant move? That's how every zombie story works.

GuestI know, it sounds impossible. But researchers found that the fungus builds a three-dimensional web of cells that wrap around every single muscle fiber in the ant's body. It's literally threading itself through the ant's legs and jaw. While it might send out some chemicals to talk to the brain from a distance, it mostly acts like a puppeteer pulling strings. It unplugs the ant's muscles from its own nervous system and starts working the limbs manually through its own fungal mesh. It forces the ant to leave the safety of its home and go on what scientists call a death march. It's not that the ant wants to go; its legs are just being walked by something else.

HostThat sounds like a nightmare. And it's all just to get the ant to go somewhere specific?

GuestExactly. The fungus is incredibly picky about the weather. It needs the heat and the moisture to be perfect for it to grow and spread. So it forces the ant to find a very specific spot that we call the Goldilocks Zone. In a big tropical forest, this is almost always the underside of a leaf, exactly ten inches off the ground, on the side of the leaf facing north-northwest.

HostTen inches? That feels way too precise. How can a fungus know the difference between ten inches and twelve inches?

GuestIt's all about the humidity at that exact height. If the ant goes a few inches higher, the air is too dry. If it stays too low, it's too cold. The fungus can feel that difference. Once the ant reaches that exact spot, the fungus triggers what we call the death grip. It sends a signal that makes the ant bite down on a leaf vein with so much power that its jaw muscles eventually just waste away. It's a permanent lock. The ant is stuck there forever, right above the trails where all its colony mates walk every day.

HostSo it’s basically a booby trap set at the perfect height. What happens once the ant is locked in place?

GuestOnce the ant is secure and dies, the fungus finishes eating what's left on the inside. It uses the hollow shell of the ant as a protective house. Then, a long, dark stalk grows right out of the back of the ant's head. It looks like a little horn or a spear. A bulb on the end of that stalk eventually bursts and rains down a cloud of spores onto the ground below. Because the fungus forced the ant to die right over a busy ant highway, the next generation of spores is perfectly placed to land on the next group of ants. It's so good at this that it can wipe out an entire colony. That's why ants have actually evolved their own kind of social health system. If they see one of their friends acting twitchy or weird, they'll pick them up and carry them far away from the nest before they can reach that biting stage.

GuestThe most chilling part is that we have found fossils of these leaf bites that are almost fifty million years old, which means this fungus has been perfecting the art of the puppet show since long before humans ever existed.

HostI'll definitely be looking at the ants in my garden a lot differently now, knowing that their little armor shells aren't nearly as tough as they look and that their brains might just be passengers in their own bodies.

GuestThe most chilling part is that we have found fossils of these leaf bites that are almost fifty million years old, which means this fungus has been perfecting the art of the puppet show since long before humans ever existed.

HostI'll definitely be looking at the ants in my garden a lot differently now, knowing that their little armor shells aren't nearly as tough as they look and that their brains might just be passengers in their own bodies.