From viruses on up, many parasites manipulate host behaviors to their whims. How these parasites adaptively learned their Machiavellian tricks is empirically inexplicable.
Endoparasitic flukes induce ants to move up onto blades of grass during the night and early morning. There the ants rigidly attach themselves with their mandibles and are consumed during the day by grazing sheep, the fluke’s final host.
Terrestrial insects parasitized by hairworms commit suicide by jumping into water, where the adult worms reproduce.