The humble fruit fly is a complex animal. It can eat, fly, navigate towards smell signals, court a mate, fight off rivals and escape predators. It can sing. For the first time, researchers have created a complete map of the 139,255 neurons and more than 50 million connections that make up its poppy-seed sized brain. The BRAIN project, which started a decade ago and involved a global team of scientists and volunteers, has published its findings across nine papers in the journal Nature. This represents an important step towards making a map of the human brain (86 billion neurons), which in turn could help treat conditions from Parkinson's to substance abuse.