Kermit the Frog famously said that it isn't easy being green, and in Living at Micro Scale David Dusenbery shows that it isn't easy being small--existing at the size of, say, a rotifer, a tiny multicellular animal just at the boundary between the visible and the microscopic. "Imagine," he writes, "stepping off a curb and waiting a week for your foot to hit the ground." At that scale, we would be small enough to swim inside the letter O in the word "rotifer." What are the physical consequences of life at this scale? How do such organisms move, identify prey and predators and (if...