As far as I know there are two types of robot flies. One of the species developed at Harvard. This project was sponsored by the well-known DARPA, which is engaged in defense research.
The fly weighs 60 grams and the wingspan is 3 cm. The principle of movement is based on the movement of a real fly. More details .
The second type was developed at the University of Berkeley, its weight is 25 grams. They have a detailed description and photos of this miracle on the site .