Sterilize your kitchen counters all you want: You’ll never be rid of the thousands of tiny organisms who live alongside us. Biologist Rob Dunn joins us to introduce us to the creatures small and smaller who inhabit the same spaces we do. His new book is called “Never Home Alone: From Microbes to Millipedes, Camel Crickets, and Honeybees, the Natural History of Where We Live” (Basic Books).