Cow/sheep liver fluke worm (​Dicrocoelium dendriticum)

These parasites start their life cycle in the cow/sheep liver where they mate and are passed out through the feces. Then, a snail comes along and eat the feces, therefore ingesting the fluke worm. As a defence, the snail secretes the worms in it's slime trail (which is exactly what the worms want it to do). The ant then comes along and eats the slime trail, where the fluke worms invade it's brain. At night, the ant climbs up onto a blade of grass and waits to be eaten by a cow where the parasite will complete it's life cycle and reproduce. 

If not eaten, at daybreak the ant goes back to normal. This happens until the ant is eaten by the cow.