One April day in 1676 a Dutchman with an enquiring mind looked through his home-made microscope at a sample of water and was amazed by what he saw: ‘an incredible number of very little animals of diverse kinds’, a world of life where none had seemed to be. That man was Antonie van Leeuwenhoek. He had just become the first person ever to see bacteria.

That pivotal moment in science is the starting point of American ecologist Rob Dunn’s eye-opening, at times jaw-dropping new book about the teeming life – from the microscopic to the all too visible – with which we share our homes. The sheer abundance of it is staggering. Dunn and his colleagues have identified some 200,000 species, of which three quarters are bacteria, found on our bodies and in dust, water and food: ‘It is the normal condition of mammals to be covered in a shaggy layer of bacteria,’ Dunn writes. ‘Even when naked, we are cloaked, and the same is true of the surfaces in our houses.’ The rest of the species are mostly fungi, with arthropods (insects and so on), plants and others making up the numbers. And these figures don’t even include viruses.

Life is everywhere in our homes. Dunn’s description of what goes on in the rich ‘biofilm’ inside our showerheads is astonishing stuff: ‘Right now, in your showerhead … tiny “pikes” [predatory bacteria] are latching on to other bacteria, drilling holes in their sides, and releasing chemicals that digest them. Showerhead