Understanding the aerodynamics that allow insects and hummingbirds to fly is the key to an invention that researchers hope will create a little buzz and a lot of flap. Biologists and technologists at the University of California, Berkeley have spent the past four years developing a tiny robot, called the Micromechanical Flying Insect, that they say will one day fly like a fly. Other projects are taking different paths, but the goal is the same: churn out tiny, nimble devices that can surreptitiously spy on enemy troops, explore the surface of Mars or safely monitor dangerous chemical spills.