Researchers are studying creatures that fly through the night in hopes of making tiny flying spies.(right) AeroVironment's DARPA-funded prototype drone made a successful test flight, lifting itself and its energy source.
The most popular of these drones are called Ravens, built by the Monrovia, Calif., company AeroVironment. They are about 4.5 feet across, weigh six pounds and can stay aloft for about an hour and a half. (More, with two cool clips of a bat flying in slow motion.)
