Unlike the wings of other birds, which are attached to the body at a single joint, hummingbirds' wings are attached to their bodies at two joints, which allows them to move their wings in a figure-eight pattern. This allows hummingbirds to fly forwards, backwards, and hover in place, which is essential for their ability to feed on nectar from flowers.

In addition to their unique wing structure, hummingbirds also have a high wing-beat frequency, which allows them to generate enough lift to maintain their hover and fly in any direction. Their muscles are also highly specialized, allowing them to generate the rapid wingbeats necessary for flight.

Overall, the combination of their unique wing structure, high wing-beat frequency, and specialized muscles allows hummingbirds to fly backwards, as well as perform other aerial feats such as hovering, diving, and flying at high speeds.