Nature sometimes writes scripts more terrifying than any nightmare. Take, for example, a curious parasite - the Cordyceps fungus.
This fungus infects insects in tropical forests, growing through the victim's body and wrapping around its muscle fibres. It controls the muscles, forcing the insect to move against its will - higher, higher, higher... The most frightening part is that the parasite does not touch the brain. Yet it turns the insect into a puppet, making it do whatever the parasite needs.
And when the victim has climbed high enough, the fruiting body of the fungus sprouts from the insect's head - to release spores and continue its work...