If drones could eat other drones, the SparrowHawk would sit somewhere near the top of the flying-robot foodchain. On a baking stretch of 110-degree dust an hour west of Phoenix, the six-rotored arachnoid rises with a menacing buzz, like a swarm of several dozen hornets' nests. Then the 14-pound, hexagonal drone lurches forward, towards its prey, a 3D Robotics quadcopter that its five-and-a-half-foot armspan dwarfs. The two drones perform a brief, mid-air dance before the SparrowHawk overtakes the quadcopter, and pulls it into a rectangular net that hangs beneath its body, tangling the smaller drone's rotors. The SparrowHawk then lowers to the ground, the captured quadcopter still twitching in its web.