In the body of a snail, a war is waging. It’s so violent that the only reason there isn’t blood everywhere is that the combatants don’t have any blood. The fighters are flatworms, simple parasites that have taken over the snail. Its body is now theirs, a shell in which they mate, cooperate, and produce more flatworms. But they don’t have it all to themselves – other colonies, and even other species of flatworms can invade the same snail. When that happens, war breaks out and the flatworms wage it with something more commonly associated with ants or humans – a caste of soldiers.
Conspiracy theories, TV thrillers and airport novels are full of the idea that the world is secretly run by a hidden society. We have come up with many names for this shadowy cabal of puppet-masters – the Illuminati, the Freemasons, and more. But a better name would be ‘parasites’.
Every animal and plant is afflicted by parasites. The vast majority are simple, degenerate creatures, small in size and limited in intelligence. They affect our health and development, and even our behaviour and culture. And by pulling the strings of key species, parasites can change the face of entire habitats.In a typical school textbook, an ecosystem consists of plants that feed plant-eaters, who in turn, line the bowels of predators. But parasites influence all of these levels, and as such, they can change the structures of entire communities.
The idea that nature is secretly manipulated by these tiny, brainless creatures is unsettling but manipulate us, they do. And by changing the behaviour of their hosts, parasites can change the face of entire habitats. Chelsea Wood and colleagues from Dartmouth College have found compelling evidence for this, by showing that a tiny flatworm can alter the structure of a tidal habitat by infecting small marine snails.