Lurking in gutters, gardens and forests, just under-foot, lies something strange. Something almost alien. They lead independent lives as single cells foraging for, and feeding on, bacteria. But when food becomes scarce they work together, in their millions, forming a multicellular ‘organism’ of individuals. In this form they’re more mobile; moving about, looking for food or new environments, displaying something akin to a brainless form of intelligence. They are everywhere, on almost every continent; but they didn’t arrive on a meteorite, like aliens bent on world domination. Instead they’ve been with us for nearly a billion years. They are the ‘slime moulds’. But wherever individuals cooperate for the greater good of their ilk, there are always cheaters; even among the slime moulds.