A parasitic fungus figured out how to take over ants’ bodies in multiple climates

There on his own free will?
There on his own free will?
Image: AP Photo/Sergei Grits
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The only thing scarier than a mind-controlling fungus is a mind-controlling fungus that has adapted its behavior to its environment.

Time to welcome Ophiocordyceps to your nightmares. It’s a genus of fungus, colloquially known as cordyceps, that lives in tropical and temperate climates. Rather than getting by in its own body, it prefers to take control of the body of a forest ant, then eat its host alive.

After infecting a host ant—usually while the insect is looking for food, a cordyceps starts to use the insect’s body like a super suit. Before it had no legs. Now it has six, which it can use to crawl to a specific spot on a plant above the ground ideal for cultivating the perfect growing conditions. After the cordyceps has purged the ant of all possible nutrients, the insect dies, and a fungal stalk grows from the ant’s head before the fungus rains its offspring down to the ground, hoping to infect more ants.

But Raquel Loreto, an entomologist at Penn State University, recently noticed something peculiar about the dying stage of this process, reports Wired. In South America, she saw infected ants would bite leaves about a foot above the ground. In Japan, she found that ants would wrap themselves around a twig much farther up, about six feet in the air. She knew it couldn’t be a coincidence—climbing up anything is abnormal behavior for ant—so she started to wonder: Was there something about the distance off the ground, or perhaps something about the material of the zombie ant’s ultimate landing spot, that was essential to the cordyceps’ survival?

Loreto took the problem to her team of researchers who gathered information about Ophiocordyceps from all over the northern and southern hemispheres, from every continent except Europe and Antarctica. Everywhere they looked, the same pattern emerged: In temperate forests, possessed ants were found dead on twigs. In tropical forests, ant corpses were on leaves.

The researchers concluded that this pattern has to do with the way trees grow in the different regions. The fungus needs to remain above the ground to release its spores. In warm tropical forests, leaves don’t fall, making them suitable targets for the ants to bite. In temperate forests, leaves cycle through the seasons, typically dropping in the autumn. In these cooler forests, the cordyceps “selectively favored the fungi to manipulate their host to bite onto twigs,” write the researchers in a paper published May 28 in the journal Evolution.

Usually when a trait like that evolves in a creature, it starts in a specific region and spreads as the species does. This doesn’t appear to be the case with cordyceps. Using genetic analyses, the researchers found that cordyceps actually evolved this same trait multiple times in various locations around the world.

The scientists don’t yet understand how the fungus can make its commandeered ant body choose between the leaf and stick. “How in the name of …whoever…does the fungus inside the body know what the difference between the leaf and the twig is?”  David Hughes, a co-author of the paper, told Wired.

For now, it seems, that’ll be a mystery to be explored in our nightmares.