- cordyceps fungi that cause ants to climb to high branches and clamp their jaws to them before dying so the fungus' can sprout out of their heads: https://www.nationalgeographic.com/animals/article/cordyceps...

- Anomotaenia brevis: a tapeworm that causes ants to live unnaturally long lives and emulate the queen ant's pheromones causes the colony to expend energy feeding the infected ants at the expense of the rest of the colony: https://en.wikipedia.org/wiki/Anomotaenia_brevis

And for another plain gross entry: a tongue-eating louse that eats and takes the place of a fish's tongue. I guess it gets to eat when the fish eats? https://www.nationalgeographic.com/science/article/tongue-ea...