Some parasites aren’t content with just hitching a ride on their host. No, they want control. Over your body, your behavior—sometimes even over your death. These creatures turn their host into a puppet, a walking zombie version of itself, purely to ensure their own reproduction.
Sound like science fiction? Unfortunately, it’s not. Here are ten parasites that literally take over the brain (or behavior) of their victim.
1. Toxoplasma gondii: the parasite that makes cats attractive (to mice)
This single-celled parasite lives in cats but reproduces via mice. So what does it do? It settles in a mouse’s brain and switches its fear of cats into… attraction. The mouse seeks out the cat. Gets eaten. And voilà: mission accomplished.
Humans can get it too (via cat feces or raw meat), and there are indications that it affects our behavior: risk-taking, guilt, even preferences. That litter box isn’t so harmless after all.
2. Cordyceps: the zombie fungus from your nightmares
This fungus infects insects, like ants, and takes over their central nervous system. It forces them to climb a high plant, bite down, and then… BOOM. A mushroom grows out of their head, spreads spores, and infects the next victim.
Yes, The Last of Us is based on this. And no: it can’t (yet) happen to humans. But never say never.
3. Leucochloridium paradoxum: the snail with disco lights in its head
This parasitic worm infects snails and crawls into their eye stalks. There, it pulses in bright colors, making the snail look like a juicy caterpillar. Birds bite. The worm ends up in their intestines—and the cycle is complete.
The snail literally becomes a flashing billboard for the parasite. No control, no escape—just bait.
4. Horsehair worms: the suicide coach for grasshoppers
The larvae of this worm grow up inside grasshoppers. Once mature, they send chemical signals to the host’s brain—which then spontaneously jumps into water. The worm crawls out. Grasshopper? Dead.
5. Euhaplorchis californiensis: the parasite that makes fish dance for birds
This parasite infects the brains of fish and influences their behavior: they swim higher, flash their bellies, make strange movements. Result: birds pick them off more easily—where the parasite reproduces.
6. Dicrocoelium dendriticum: the parasite that makes ants climb to their death
This worm infects ants and forces them to climb to the top of blades of grass in the evening—exactly where grazing sheep or cows might bite. If that doesn’t happen, the ant returns to the colony during the day and climbs again the next night.
7. Sacculina: the parasite that turns a crab into a broodmare
This barnacle-like parasite attaches to crabs, grows inside their body, and takes over their reproductive system. Male crabs develop female characteristics, and *all* infected crabs start caring for the eggs of… the parasite.
The crab becomes a sort of nanny for something taking it over from the inside out. Creepy with a capital C.
8. Hymenoepimecis argyraphaga – the spider hypnotist
This parasitoid wasp from Central America has a favorite host: the Plesiometa argyra spider. It lays an egg on the spider’s back, after which the larva hatches and feeds on the spider’s hemolymph – slowly, without killing it immediately. So far, standard parasitoid wasp behavior.
But then comes the bizarre part: when the larva is ready to pupate, it injects a chemical substance into the spider that causes it to completely change its web pattern. Instead of a catching web, the spider now spins an extremely sturdy “hammock web,” perfectly suited for the weight and protection of the wasp cocoon. Only then does the larva suck its host dry – until death follows – and spins itself safely into the web the spider made for it.
9. Ampulex compressa – makes zombies out of cockroaches
This emerald wasp has a very sinister ritual. It hunts cockroaches and stings them twice with surgical precision: first to disable their escape reflex, then in their brain to completely eliminate the will to flee. The result: a living cockroach that still registers everything but no longer resists.
The wasp then literally leads its ‘zombie’ by its antennae to a pre-dug burrow. There, it lays an egg on its abdomen, seals the entrance, and leaves. The cockroach waits calmly until the larva hatches, burrows inside, and eats it alive – from the inside out.
10. Spirometra: a tapeworm that prefers to invade your brain
This tapeworm sometimes ends up in humans (via raw frogs or snakes) and then crawls… yes, really… to your brain. There it causes the rare condition sparganosis, resulting in hallucinations, paralysis, and madness.
It rarely happens. But the thought of a parasite seeing your brain as living space is enough for a sleepless night.
Parasites aren’t just hitchhikers. Some are masterminds that take over entire lives, rewrite behavior, and use bodies as temporary hotels. They manipulate with precision, using an evolutionary strategy so refined you almost have to respect it.
Almost. Because however fascinating—these are nature’s horror films. Only real.
