If the host were to bake in the heat of the direct sun, the parasites would die with it. When evening comes again, they send the ant back up a blade of grass for another try. After the ant finally tumbles into a cow's stomach, the flukes burst out and make their way to the cow's liver, where they will live out their lives as adults. Far from simply being along for the ride, parasites may be one of nature's most powerful driving forces. At the Carpinteria salt marsh, Kevin Lafferty has been exploring how parasites may shape an entire region's ecology.
Birds release the fluke's eggs in their droppings, which are eaten by horn snails.
The eggs hatch, and the resulting flukes castrate the snail and produce offspring, which come swimming out of their host and begin exploring the marsh for their next host, the California killifish. Latching onto the fish's gills, the flukes work their way through fine blood vessels to a nerve, which they crawl along to the brain. They don't actually penetrate the killifish's brain but form a thin carpet on top of it, looking like a layer of caviar. There the parasites wait for the fish to be eaten by a shorebird. When the fish reaches the bird's stomach, the flukes break out of the fish's head and move into the bird's gut, stealing its food from within and sowing eggs in its droppings to be spread into marshes and ponds.