Yup, you knew it was coming eventually. Biological zombies.
Now, I’ll admit that I honestly am not that big a fan of the whole “infection” zombie, much preferring the more horror-esque zombies for my games. Necromancy, raising the dead, classic D&D zombies, though perhaps with a few interesting twists on how it relates to the soul.
But that doesn’t mean you have to go full zombie with what I’m going to talk about. In fact, it may be even more horrifying if you don’t, instead just having everyone infected simply be… off, somehow.
So, let’s talk about biological zombies.
Turns out there’s several kinds.
The first, which a lot of people are probably already aware of (and if not, strap yourself in, it’s gonna be a bumpy ride), is the one created by fungi. Cordyceps, to be specific.
This spores of this fungal genus infect the specific species of insect or arthropod they evolved for, the mycelium invading the host and messing with their brain, and making their victims climb high up before gripping whatever structure their climbing on with a literal deathgrip.
There, the fungus finishes slowly replacing host tissue, killing the host, and grows out of the body to spread its spores to other members of the species.
Not a pretty picture, is it?
It’s not the only form of life to brainwash another species as part of its reproductive cycle.
There’s also the Jewel Wasp, which stings cockroaches in the brain, the venom working to eliminate their urge to escape. So the roach calmly continues to clean itself as the wasp bites off an antennae, and then idly lets the wasp lead it into a burrow the wasp made.
The wasp lays a single egg on the roach, and then seals the burrow, Cask-of-Amontillado-style, with the living roach still inside. The roach just sits there, not a care in the world, while the egg hatches and burrows into it, slowly eating its organs (saving the vital organs for last, of course, so the roach stays alive as long as possible while it’s being eaten from inside).
Eventually, having eaten the cockroach alive from the inside out, the new wasp digs its way out of the burrow to continue the cycle.
These aren’t the only examples, either. There’s a protist called Toxoplasma Gondii that makes rats seek out cats rather than avoid them in order to get the rat eaten so the parasite can reproduce inside the cat. Make what conclusions you will about the fact that it has been also found in humans.
However, if you plan on using these sorts of things in your campaign setting, there are a few things to keep in mind: for one, those sorts of parasites tend to be very specific, especially when it comes to the delicate workings of altering brain chemistry. Something that might make one species behave a certain way might make another species simply go crazy.
For another, humans have very large and very complex brains, on top of being much larger than the typical targets of those brainwashing parasites in general. This means we would likely be more resistant to whatever venom they used, if not simply have it affect us in other unexpected ways even if we were pumped full of the stuff.
Odds are, if something were to affect us in a reliable way that is useful to the parasite, it would probably be larger and/or target humans or humanoids specifically.
So, if you want to introduce biological zombies to your local rpg campaign, without resorting to necromancy or otherwise using magic to raise the dead, maybe it’s time for your players to take a walk through a forbidden mushroom forest.
Where they can find the overgrown remains of a town, and the stiff remains of the former villagers on the rooftops.
Good luck on your Fortitude saves.