http://www.anglingmasters.com/10-bizarre-behaviors-of-parasites.asp

The lancet fluke finds its way into snails while they are feeding on cow feces. The fluke remains in the snail until it matures into a tad-pole like creature, which is literally coughed out by the snail in a coating of thick mucus. This mucus is considered a delicacy for ants but after feeding on the infested mucus they become the new hosts. Once infected the ants leave their colony every night to attach themselves bottom side up to a tall blade of grass with their clamping mandibles. It waits in this manner until it is finally eaten by a cow. Once the ant has been ingested the parasite breaks out and swims through the digestive tract until it reaches its new home, the bile duct. From here new eggs are released and allowed to exit through the digestive tract inside the feces, which will then be eaten by snails to continue the cycle.

Now *that* is a life plan.