Military researchers are at work on another revolution in the air: shrinking unmanned drones ... to the size of insects and birds. The drones in development ... 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," said Greg Parker, an aerospace engineer, as he held up a prototype of a mechanical hawk that in the future might carry out espionage or kill. An explosion in aerial drones is transforming the way America fights and thinks about its wars. Predator drones ... are by now a brand name, known and feared around the world. But far less known is the sheer size, variety and audaciousness of a rapidly expanding drone universe, along with the dilemmas that come with it. The Pentagon now has some 7,000 aerial drones, compared with fewer than 50 a decade ago. Within the next decade the Air Force anticipates a decrease in manned aircraft but expects its number of "multirole" aerial drones like the Reaper - the ones that spy as well as strike - to nearly quadruple, to 536. Already the Air Force is training more remote pilots, 350 this year alone, than fighter and bomber pilots combined. "It's a growth market," said Ashton B. Carter, the Pentagon's chief weapons buyer. The Pentagon has asked Congress for nearly $5 billion for drones next year, and by 2030 envisions ever more stuff of science fiction: "spy flies" equipped with sensors and microcameras to detect enemies