This parasite relies on 3 species to complete it's lifecycle. From http://io9.com/12-real-parasites-that-c ... -461313366"The Lancet liver fluke Dicrocoelium dendriticum has a very busy life. As an adult it spends its time in the liver of a cow or another grazing mammal. Here it mates and lays eggs, which are excreted in the host's feces.
A snail eats the poo, taking in the eggs at the same time. The eggs hatch in the snail and make their way into its digestive gland, where they asexually reproduce. They then travel to the surface of the snail's body. As a defensive maneuver, the snail walls the parasites up in cysts and coughs up the balls of slime...doing exactly what the parasites wanted it to do.
An ant comes along and gobbles up the fluke-laded slime balls. The flukes then spread out inside of the ant, with a couple of them setting up shop in the insect's head. When night approaches, the flukes take control. They make the ant climb up a blade of grass and hold tight, waiting to be eaten by a grazing animal. If the ant is still alive at dawn, the flukes release their control and the ant goes about its day like normal (if the ant baked in the sun, the parasite would die, too). At night the flukes take over again and the cycle repeats until the ant becomes cattle food."