Ants on Grass Blades

The lancet liver fluke uses ants as transport. Inside an infected ant, one larva reaches the ant's nervous system and changes its behavior. At dusk, the ant climbs a blade of grass and clamps down.

That makes it more likely to be eaten by grazing sheep or cattle, where the fluke can continue its life cycle. One parasite stage turns an ant into a delivery system.

The fluke's goal is to get its ant eaten by a grazing sheep — and timing is everything. Each evening, the brain-riding larva drives the ant up a grass blade and locks its jaws shut, right where sheep nibble at dawn and dusk. Each morning, if no sheep has come, the ant climbs down and goes about its day. The hijacking switches on only during the hours when a sheep is most likely to be chewing.