Marvel’s latest film tells the origin story of Venom – a sentient alien 'Symbiote' that takes over the body of journalist Eddie Brock, played by Tom Hardy. The alien parasite bonds with Brock, transforming him into a powerful monster. Obviously this is science fiction. But, the concept of parasites that attach to a host’s body creating a symbiotic bond is pretty routine and Symbiote-like creatures exist all around us.