Many insects can hover, or stay in one spot in the air, doing so by beating their wings rapidly. The ability to do so, though, is complex; requiring the use of sideways stabilization as well as the lift necessary to overcome the force of gravity. The lifting force is caused by the downward stroke of the wings. As the wings push down on the surrounding air, the result reaction force of the air on the wings force the insect up. The wings of most insects are evolved so that, during the upward stroke, the force on the wing is small. Due to the fact that the upbeat and downbeat force the insect down and up respectively, the insect oscillates and winds up staying in the same position.