In such species as flies and bees, the muscles that allow flight are not even attached to the wing base! Instead, they attach to the chest by joints that serve as a kind of hinge, while the muscles that lift the wing upwards are attached to the upper and lower surfaces of the chest. When these muscles are contracted, the chest surface flattens and draws the wing base down. The lateral surface of the wing provides a support function and permits the wings to rise. The muscles establishing downward movement are not attached directly to the wing, but operate along the length of the chest. When these muscles are contracted, the chest is retracted in the opposite direction, and the wings are thus drawn downwards.
The wing joint is formed of a special protein known as resilin, which possesses superb elasticity. Since its features are far superior to those of natural or synthetic rubber, chemical engineers are trying to reproduce this substance, in laboratories. In flexing and contracting, resilin is able to store almost all of the energy exerted on it; and when the force pressing on it is lifted, it is able to give back all that energy.