Parasites in fiction are stories about creatures and bad things that live inside people's bodies, or animals' and plants' bodies, that try to take over control and make them do bad things. These creatures usually come from other planets or faraway places, and they make their victims act against their own will. Sometimes, the parasites are like small bugs or worms, but other times they can take the shape of a monster or a human being. Parasites in fiction can also be used to tell scary stories about how people can lose control of their bodies because of these creatures.