Twelve real parasites that control the life cycles and actions of their hosts:Parasites That Control Their Hosts
Given these examples from earthly biology, maybe certain “puppet master” entities from science fiction don’t seem so far-fetched. The puppet masters in Heinlein’s novel of that title are essentially disembodied brains that attach themselves to the spinal columns of their victims and take control of the hosts’ bodies and brains. In STAR TREK: THE NEXT GENERATION and DEEP SPACE NINE, we meet more benign symbionts from the Trill culture, which get surgically inserted into a humanoid body and merge their minds with those of their hosts. Joining with a symbiont is considered an honor. In this partnership, the personality of the host isn’t obliterated but blended with that of the possessing entity.
And then there’s THE HOST, by Stephenie Meyer. While I haven’t read it, it sounds very different from her Twilight series. The creatures that possess human hosts in this novel are disembodied intelligences, not physical entities like the other two species just mentioned. According to the blurb, the possessed protagonist doesn't lose her own personality as normally happens.
Most of the parasites listed in the article above infest invertebrates such as insects, worms, and snails. Imagine scaling up these phenomena to human size—producing, for example, a creature that uses us as incubators for its young and chemically inspires the human host with devoted love for the parasite babies. Willing human males become hosts for alien larvae in Octavia Butler’s “Bloodchild,” but they aren’t mind-controlled. Butler’s characters accept this arrangement in a rational bargain; imagine pheromones that emotionally compel people to embrace the status of incubator. Would chemically induced love for the parasitic (or symbiotic) infants be “real love”?
Margaret L. CarterCarter's Crypt