Parasitic worms have armies, and produce more soldiers when needed

In estuaries around the world, tiny trematode worms take over the bodies of aquatic snails. These parasitic flatworms invade the snail's body and use its systems to support their colony, sometimes for over a decade, "driving them around like cars," according to senior author Ryan Hechinger, professor of marine sciences at Scripps Institution of Oceanography at the University of California San Diego.