You can hear cicadas from all directions as you make your camp at the base of a large tree. They are noisy and inescapable, but at least that will make staying awake through your watch easier.
Suddenly, everything goes quiet. You’ve been doing this long enough to know that sudden silence is never a good sign.
Right on cue, there is rustling in the foliage and the crackling of branches broken by whatever is heading your way. You’re ready to face down whatever monstrosity emerges from the trees, but instead, a man bursts into the clearing. He looks confused, moves erratically. He heads toward you, but at the same time doesn’t seem aware that you are there. You try yelling for his attention, but he gives no indication that he can hear you. You watch, bewildered, as he keels over, and you notice a tendril that snakes out of the back of his neck. As he collapses to the ground, a thick cloud bursts from the stalk, settling on the ground, nearby plants, and your skin.
You have just encountered cordyceps and yes, it is a nightmare.
Unlike the awful flora and fauna we’ve covered so far, cordyceps is very real. This genus of parasitic fungi infects bugs–each species of cordyceps relies on a different insect as part of its horrifying life cycle, from ants to tarantulas to walking sticks. An insect is infected with spores, which grow and replace tissue and innards with fungus. Cordyceps also gets its host to do what it wants–it gets the insect to grab on to a leaf or stick, where it will die. Its exoskeleton becomes protection for the fungus inside as it continues growing, until it breaks through to release spores and infect more insects.
There aren’t any species of cordyceps that affect anything other than insects, but the idea of this zombie-making fungus showing up in animal or human hosts has inevitably come up in fiction and video games. Mammalian immune and nervous systems would be way more complicated for a fungus to hijack, but assuming it had the same life cycle, humans would be infected by spores and the growing fungus would chemically take over thought and motor functions in the interest of maximizing its chances of spreading. This would mean finding a populated spot to release spores in hopes of infecting as many people as possible.
To avoid becoming a fungus zombie, the best bet would be to take a page out of the ants’ playbook. Ants are aware of the erratic behavior that comes with cordycep infection (cordyception?) and will take affected ants far away so spores don’t wipe out the entire colony. So, if there were a cordycep that could infect humans, step one would probably be to isolate them and try to minimize the spread. Watching for weird behavior as the fungus inserts itself between brain and body functions would be crucial, and isolating the infected so they don’t infect others. And if you get infected? Well, unless you have antifungal medication handy, you’re probably doomed to die a fungus zombie.