WRIGHT-PATTERSON AIR FORCE BASE, Ohio — Two miles from the cow pasture where the Wright Brothers learned to fly the first airplanes, military researchers are at work on another revolution in the air: shrinking unmanned drones, the kind that fire missiles into Pakistan and spy on insurgents in Afghanistan, to the size of insects and birds. The base’s indoor flight lab is called the “microaviary,” and for good reason. The drones in development here are designed to replicate the flight mechanics of moths, hawks and other inhabitants of the natural world. “We’re looking at how you hide in plain sight,”...