You’ve seen them. Those twitching, clicking nightmares that haunt the ruins of Boston and Seattle. If you’ve played the games or watched the HBO adaptation, you know that infected The Last of Us creatures aren't your typical Hollywood zombies. They don’t want your brains. They aren't magical. Honestly, they’re basically just meat puppets for a very real, very ambitious fungus.
The most terrifying part about the Cordyceps Brain Infection (CBI) isn't even the jump scares. It’s the fact that Naughty Dog didn’t just make this up out of thin air. They took a look at the natural world, saw how the Ophiocordyceps unilateralis fungus turns ants into mindless drones, and simply asked, "What if it jumped to us?"
The Four Stages of the Cordyceps Nightmare
Most people think of the infected as one big group. That’s wrong. It’s a progression. A literal biological takeover that happens in distinct, gruesome phases.
When a human breathes in spores (in the game) or gets bitten (in both the game and the show), the fungus starts its work. It doesn't kill you. Not at first. It wraps itself around your brain, hijacking your motor functions while keeping your body alive. You're still in there. Somewhere. That’s the true horror of the infected The Last of Us lore—the idea that the person is a passenger in their own body.
Runners: The Panic Phase
This happens within 24 to 48 hours. Runners are fast. Too fast. They still look human, which makes them the hardest to deal with psychologically. You’ll see them sobbing or moaning, but their bodies are sprinting at you with frantic, jerky movements. They haven't lost their sight yet, so they’ll spot you from across a parking lot. It’s a numbers game with them. One Runner is a nuisance; five is a death sentence.
Stalkers: The Creepers
Between a week and a year of infection, things get weird. The fungus starts growing out of the head, usually pushing through the eye sockets. This is the Stalker phase. These guys are the worst because they actually have the cognitive leftovers to hide. They won't just charge you. They’ll duck behind a wall, wait for you to pass, and then rip your throat out. In The Last of Us Part II, the Stalkers are arguably the most hated enemy because they don't show up on "Listen Mode." They just wait.
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Clickers: Evolution of Sound
You know the sound. That sharp, rhythmic clicking. This stage occurs after at least a year. The fungal growth has completely blinded the host, splitting the skull open like a rotten fruit. To navigate, they use echolocation. It’s effective. Clickers are significantly stronger than Runners because the fungal plates act as a sort of organic armor. If one grabs you and you don't have a shiv or a brick, you're done.
The Big Boys: Shamblers and Bloaters
If an infected person survives for years—usually in wet or cramped environments—they become a Bloater. These are the tanks. They’re huge, slow, and covered in thick, calcified fungal plates that can shrug off shotgun blasts. They don’t just bite; they throw sacks of mycotoxin that explode into acidic clouds.
Then you have Shamblers. Introduced in the Seattle chapters of the second game, these are a variation caused by the high humidity of the Pacific Northwest. They don’t have the raw strength of a Bloater, but they release massive bursts of gaseous acid when they get close. Even after you kill them, they explode. It’s a final "screw you" from the fungus.
Is the Science Actually Real?
Neil Druckmann and the team at Naughty Dog famously cited a segment from the BBC’s Planet Earth as the primary inspiration for the infected The Last of Us concept. In the clip, narrated by David Attenborough, a fungus infects an ant’s brain and compels it to climb to a high point before sprout-killing it to spread spores.
In reality, Ophiocordyceps exists. It’s real.
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But could it jump to humans?
Experts like Dr. Ian Will from the University of Central Florida have noted that while the jump from insects to mammals is a massive evolutionary leap, the "zombie" mechanic isn't entirely fantasy. However, our body temperatures are generally too high for most fungi to survive. This is why the HBO series introduced the idea of global warming—the fungus evolved to survive higher temperatures, eventually making the jump to us through contaminated flour. It's a terrifyingly plausible tweak to the lore.
Why We Can't Look Away
There is something deeply unsettling about the fungal aesthetics. It’s called "body horror." Unlike vampires who stay pretty or ghosts who are invisible, the infected The Last of Us monsters are a visceral reminder of our own mortality and the indifference of nature.
The fungus isn't evil. It doesn't hate Joel or Ellie. It just wants to grow. It wants to find a high point, settle down, and spread its life cycle to the next host. This lack of malice somehow makes the violence feel more hollow and terrifying. You aren't fighting a villain; you’re fighting an ecosystem that has decided humans are no longer the top of the food chain.
How to Handle the Infected (In-Game Strategy)
If you're jumping back into the Remastered versions or the PC port, you need to change your mindset based on what you’re facing.
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- Against Runners: Use your environment. A single bottle or brick can stun them long enough for a melee kill, saving your precious ammo.
- Against Clickers: Stealth is your only friend. Crouch-walk at the slowest possible speed. If you have a bow, aim for the "soft" spots not covered by plates, though a headshot is always the goal.
- Against Stalkers: Don't wait for them to come to you. If you hear that wet, scuttling sound, pull out a shotgun or a submachine gun and clear the corners. They thrive on your hesitation.
- The Spore Factor: In the games, keep an eye out for floating particles. If you see them, your gas mask is mandatory. In the show, watch for the "tendrils" in the ground. One wrong step on a fungal patch can alert a horde miles away because of the interconnected mycelium network.
The Rat King: A Fungal Nightmare
We have to talk about the Rat King. Found in the basement of a hospital in Seattle, this is a "super-organism." It’s what happens when dozens of infected are trapped in a small space for twenty years. They literally fuse together.
It represents the peak of what the Cordyceps can do. It’s a mass of Clickers, Bloaters, and Stalkers all acting as one giant, fleshy tank. It’s the only part of the game that feels like a true "boss fight" in the traditional sense, but it serves a narrative purpose. It shows that the longer the infection lasts, the more the human form disappears entirely, replaced by something alien and collective.
Survival Insights for Your Next Playthrough
The infected The Last of Us creatures are more than just enemies; they are a ticking clock for humanity. To survive them, stop thinking like a soldier and start thinking like a scavenger.
- Prioritize Silence: Most encounters with Clickers can be bypassed entirely. You don't get XP for kills in this game; you get survival for being smart.
- Resource Management: Only use your molotovs on groups or Bloaters. Using a molotov on a single Runner is a waste of alcohol and rags you’ll need for medkits later.
- The Environment is Key: High ground doesn't always help against Stalkers, but it’s a lifesaver against the mindless rush of Runners.
- Audio Cues: Play with headphones. The sound design in these games is world-class and will tell you exactly where an infected is before you see it.
The world of The Last of Us is bleak, but understanding the biology of your enemy is the first step toward reclaiming a bit of that world. The Cordyceps is a master of adaptation. You have to be faster. You have to be smarter. Most importantly, you have to stay quiet.