There is no shortage of zombie movies. As we move into October, I expect a lot of zombie movies to tour on TV. Many are fascinated by the idea of something taking hold of their body and controlling it against their will. Sounds scary enough, but could zombies actually exist in the wild? While what we see in the movie is very far-fetched, there’s no question that the zombies are real.
Meet the parasitic fungus with the scientific name that turns the tongue: Ophiocordycepslateralis. He has a unique way of reproducing. The fungus infects carpenter ants in the tropical forests of Thailand and turns them into zombies. An ant infected with this fungus leaves its nest around noon, a special time for this ant to wander. It will then move at random. This is also bizarre behavior for this ant as it usually follows well-defined chemical traces. The ant then locates a plant not far from the nest and climbs to a height of about 25 centimeters, where it will bite into a central vein of the plant leaf and cling to it.
A few days later, a mushroom sprang up from the back of the ant’s head, like in an “Alien” movie. The fungus develops fruiting bodies and spreads fungal spores, passing on the fungal DNA to a new generation. The spores will infect future carpenter ants when they feed and the cycle will repeat itself.
A quick examination of the plants near the ant nest reveals a graveyard of tiny ant bodies still clinging to their leaves, with fungal pests growing from their heads. A frightening spectacle if you take the time to contemplate what happened. A sight like this would almost certainly force the first to observe it to stop and wonder what caused such an event on Earth?
The answer lies in DNA. The ant did not come out of the nest at midday or climb the plants to bite the veins of the leaves; it was the mushroom in the ant costume. This is called the extended phenotype.
The ant is actually the fungus, by extension. When the ant bites the vein of the leaf, about half of its brain cells are not its own, and the fungal cells spread into the muscle tissue of the ant. When analyzing the DNA of the fungus, scientists discovered many genes that produce enterotoxins, which are known to impact chemical communication.
Behavior in biology often comes down to neurochemistry. Once the ant is dead, the fungus turns off the zombie control genes and turns on the genes that will digest the ant, grow the fungus and produce the fungal spores. The fungus, ruled by its own DNA code, zombified the ant so that it could walk to the perfect spot to release its spores. Inside this tiny spore that will infect another ant is the fungus’ DNA code. The code has all of the directions needed to repeat this story.
A better question might be: is the mushroom just the zombie of its own DNA code?
Dr Jack Brown is the President of the Science Division of the Collège junior de Paris.