Drone advocates neglect additional features looming on the horizon. First, drones will be arriving in all sizes and shapes. Newspapers and television tend to illustrate drones resembling those toy airplanes that flew in endless circles. Drones are acrobatic machines, capable of being maneuvered amid trees in forests and buildings dotting an urban skyline. Some are called micro-aviaries, as they can emulate the motions of hummingbirds. Scientists are now completing work on nano-drones, which will masquerade as bees or house flies. Not to worry. The naked eye will not recognize them, unless they travel in swarms.