How about something a bit more cheery? The Honeyguide, for example. It has a unique call that it only makes when it (a) knows where a bees nest is and (b) can see some humans nearby. It goes to the humans, makes its special call, flies a bit closer to the nest and repeats, until the humans find it. Then the humans crack open the nest, nick all the honey, and leave a few chunks of nest out so the bird can have a few grubs. Happy symbiosis. Unless you are a bee, then it's a horror story like two giant evil monsters join forces to destroy your city or something.
Oh also the Honeyguide lays its eggs in other birds' nests whereupon the chick brutally murders the foster family's own children. But hey, it's a step up from Zombie Fungus, isn't it?
