They’re not quite the classic brain-eating, gormless slow-shufflers of horror movies, but for some species, the zombie threat is very real. The culprit? Parasites: small organisms with complex life cycles that set up camp inside their animal hosts. These gruesome body-snatchers are able to control the animals’ minds, using them as living-dead puppets and steering them to positions of optimal benefit.
One classic case is the zombie ant. The parasite is a mind-controlling fungus (Ophiocordyceps camponoti-rufi pedis) that manipulates carpenter worker ants into straying far enough from the colony that their social immunity is impaired. The fungus makes the ant bite down underneath a leaf, where it is anchored until it dies, then the ant’s corpse is used by the fungus to grow. The fungus also releases spores that rain down and infect more ants, and so the nightmare continues.
Killifish in California have been discovered to play host to a mind-sucking parasite that alters behaviour in order to further its own species. These zombie fish are infected with a fluke, a small, parastitic worm that reproduces in the guts of sea birds. The flukes are able to limit the production of serotonin in the fish’s brain, which makes the fish very restless. Ordinarily shy of the surface and its dangers, infected fish actively swim near and even flick the water surface, greatly enhancing the changes of getting plucked out and eaten by a bird.
One insect group responsible for zombifying its victims and turning them into mindless drones are wasps. The jewel wasp (Ampulex compressa) injects venom directly into the brains of cockroaches, targeting two specific locations that render the roach’s free will useless. The wasp leads the cockroach to a burrow and lays an egg on the roach’s abdomen. The zombie roach only dies once the egg hatches and the larva devours it piece by piece.
Another wasp species, the green-eyed wasp (Dinocampus coccinellae), makes light work of harnessing the power of the ladybird. The wasp lays her eggs inside the bug, and new evidence suggests that a virus also attacks the ladybird’s brain, paralysing and enslaving it as a zombie babysitter. The larva emerges and weaves a cocoon between the ladybird’s legs so the paralysed bug acts as a bodyguard until the larva is ready to leave. Amazingly, a quarter of ladybirds recover from their zombification!
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