Toxoplasma gondii is a parasitic protozoan borne by cats that causes mice to lose their fear of felines and infects roughly a third of people worldwide. A parasitic fungus, Ophiocordyceps unilateralis, controls the minds of ants and bids them to climb, as seen in the BBC documentary Planet Earth. The fly Apocephalus borealis lays its eggs in bees, a parasite that causes bees to turn to wildly-flying zombees.
Some of you are probably just desperately clawing for some solace in the idea that these things are oddities of the natural world, that they are outliers. And that point of view is understandable because, by their nature, parasites are quite small and they spend a lot of time inside the bodies of other things. They're easy to overlook, but that doesn't mean that they aren't important... Manipulation is not an oddity, it is a critical and common part of the world around us.”
...I think this is part of what makes parasites so sinister and so compelling. We place such a premium on our free will and our independence that the prospect of losing those qualities to forces unseen informs many of our deepest societal fears. Orwellian dystopias and shadowy cabals, and mind-controlling supervillains—these are tropes that fill our darkest fiction. But in nature, they happen all the time.