The zombie pandemic is alive and well – among ants, anyway.
A new study published in Current Biology in late October identifies the origins of a fungus that turns ants into zombies. Apparently these fungi got their start on the zombie apocalypse (for bugs, that is) with beetles, and they're still going strong.
Wait, What is This?
It's the fungus Ophiocordyceps, and it's after ants. According to reporting from the New York Times, a marching ant might occasionally come in contact with a fungal spore. This spore would then stick to the ant's body and deposit a fungal cell inside it, which grows into Ophiocordyceps. This cell feeds on the ant from the inside out, multiplying to create new cells while the ant proceeds with its daily life, finding food to bring back to its colony's nest.
Eventually, the fungus composes about half of its host ant's body, and when it finishes feeding, the fungal cells form a mat inside the ant's body and insert "needlelike projections" into the insect's muscle cells.
And that's when the zombie transformation completes.
The fungus transmits chemical signals to the host's brain, prompting it to leave its nest and climb onto an above-ground leaf. The ant then bites down on the leaf, dies, and grows a stalk out of its head, which drops fungal spores onto the ant trails below – beginning the zombie cycle all over again.
As David Hughes, Ophiocordyceps expert at Pennsylvania State University, told the New York Times: "The ants are walking over a minefield."
Where Does this Fungus Come From?
Scientists have known about this fungus for decades, and according to a 2010 study published in Biology Letters, this fungal genus has been making zombies of insects for at least 48 million years. But researchers have just begun to unravel how the zombifying process actually takes place.
Joao Araujo, research fellow at Japan's University of the Ryukyus, analyzed the DNA of more than 600 fungal species that feed on dead plants and insects. Araujo used comparisons of these fungi's genetic sequences to draw a fungal family tree, which revealed that all Ophiocordyceps species come from a single common ancestor.
That ancestor fungus began its work with beetle larvae. Because beetles are solitary creatures, there was no need for the fungus to control the creature's mind, directing it away from its nest or colony. Ants, however, present a different challenge, as they live in groups and get rid of any individuals exhibiting signs of illness.
"They kick them out of the nest, or they kill them and rip them apart," Araujo told the New York Times. For that reason, the zombifying fungus has to control an ant's mind to complete its task.
How Does this Happen?
For the most part, this is still a mystery.
Scientists know the fungus sends chemical signals to its host's brain, but they don't know what the chemical is or how it causes the ant to leave its nest. Or, as Hughes worded it, "we still haven't found the smoking gun."
However it happens, it's clear Ophiocordyceps adapted well. It evolved to ensure its ant hosts would depart from their colonies, but only enough to avoid getting killed.
According to Araujo, the fungus "had to develop a way to make the host leave the nest, but not so far, because they still had to shoot spore and infect new hosts," according to the New York Times.
Araujo went on to add there are likely hundreds of undiscovered species of this zombifying fungus, and scientists will continue uncovering them for decades, if not forever.