What is cordyceps?
If you're not asking, then you haven't been watching HBO's grim zombie-apocalypse drama, "The Last of Us," an enormous hit (4.7 million viewers the first day) since it began airing Jan. 15.
And if you are asking, do you really want to know?
"Human beings might think it's disgusting," said Abdul Aqeel, assistant professor of microbiology at Bergen Community College.
Based on the popular 2013 video game, "The Last of Us" (new episodes drop 9 p.m. Sundays) takes place in a blasted hellscape that was America.
Tough-guy Joel (Pedro Pascal) and scrappy 14-year-old Ellie (Bella Ramsey) have to navigate a ruined country, laid low by pandemic. Only this particular infection has turned the majority of humans into twisted, frothing mutants with hideous growths sprouting from their brains, mouths, and bodies.
Cordyceps, it's called. And cordyceps — this is the show's master-stroke — is a real thing.
Could it do what this show's nightmare scenario is suggesting? No. Full stop. But the real details about cordyceps are nasty enough.
Cordyceps horror show
Cordyceps is a parasitic fungus. Or rather, it's a family of about 150 species of fungi that commandeer insects — notably ants — arthropods like spiders, and in some cases other fungi as hosts.
But it's how they do it that is so creepy.
"Essentially what happens is the spores land on the host insect, and then start growing within the insect," said Luke Smithson, trustee for the New Jersey Mycological Association (Mycology is the study of fungi).
The fungi produce toxins that affect the insect's brain, and start to alter its behavior patterns.
"In some species, they will hijack the insect's nervous system, force it to climb onto some sort of perch — usually the branch of a tree trunk that overhangs the other insects — and then the fungus will kill the insect and sprout its fruiting body from the insect. And then it will rain its spores down over the top of the healthy insect population."
Like the cordyceps monsters in "The Last of Us" — called Clickers in the show — the cordyceps fungi is driven to propagate its own species.
But like the residual humans in the HBO show, the insects victimized by cordyceps are not taking it lying down.
"What's impressive is that in at least some insect societies, the insects will recognize one of the infected by the way it's acting, and actually kill that insect and drag it away from the nest to try to stymie the infection," Smithson said.
Everywhere you want to be
Cordyceps is most widespread in the tropics, but species also appear locally, in places like Pennsylvania and New Jersey. What makes cordyceps different from the other 1.5 million species of fungi is their nutrient needs. "They cannot eat dead matter," Aqeel said. "Other fungi eat dead matter. Saprophytic, they're called. These fungi need fresh body materials to survive."
Not all cordyceps species are toxic, by the way. Some are eaten as delicacies.
And even the toxic ones may have potential benefits to humans. Some are used in alternative medicine. Some have been studied by pharmaceutical companies. After all, penicillin, too, began as a fungus.
"They're looking at the potential to extract this toxin to defeat some human diseases," Aqeel said.
The premise of the HBO show — laid out in an episode one prologue — is that global warming has caused the cordyceps to mutate, within 20 years, into an organism that prefers human hosts. Thus it cleverly taps into two of 2023's prevailing fears: pandemic and environmental change. By the second episode, it's tapped into another one: incipient fascism.
But in fact, fungi don't mutate that quickly. They are not quick-change artists, like viruses.
"In order for this fungi to attack humans, they would need millions of years of evolution," Aqeel said. "It wouldn't just happen overnight."
As a matter of fact, evolutionarily speaking, fungi are closer to humans than to plants — by about a billion years.
"In terms of our last common ancestors, we divided from fungi much more recently than we divided from plants," Smithson said. "Plants create energy by photosynthesis. Fungi are like animals. We have to eat things for energy."
So fungi are our long-lost cousins. Hooray! That's not to say that we shouldn't worry about them. Some varieties, less grotesque than cordyceps, are in fact a lot more dangerous to us.
"We should worry about fungi that make us allergic, molds and Aspergillus," Aqeel said. "These are toxic, so a lot of people are allergic and maybe die from them. Those are things that affect human beings."
This article originally appeared on NorthJersey.com: Cordyceps: ’The deadly parasite from ‘The Last of Us’ is real