Imagine a parasite that lodges in the brain and starts to exert a sinister influence over your behaviour. It affects how sexy you feel, or how angry or frightened, even how you dress. Not only does such a creature exist – but it may have infected up to 40 per cent of the population.
Perhaps the most famous example of such “zombie reprogramming” (or neuroparasitology, to give it its proper name) comes from a parasitic wasp that attaches its eggs to the belly of an orb spider. Larvae emerge and release chemicals that zombify the spider, which stops spinning its normal spiral web and instead starts producing a cocoon to hold the baby wasps when they emerge.
Then there is a parasitic fungus called Ophiocordyceps. After being infected with its spores, the Camponotus ant, found in the Brazilian rainforest, develops an unsteady gait, wandering off its normal paths. The creature has become compelled to find a remarkably precise location: a tree about 25cm above the usual ant trails, facing northwest. At noon, it will clamp its jaws on to a leaf in a death grip. Within six hours, it will be dead. A few days later, a tube will sprout from the ant’s head. This is the fruiting body of the fungus that emits the spores, which will infect a new generation of ants..