To better grasp the visuomotor control system underlying insects' height and speed control, we attempted to interfere with this system by producing a major perturbation on the free flying insect and obsering the effect of this perturbation. Honeybees were trained to fly along a high-roofed tunnel, part of which was equipped with a moving floor. The bees followed the stationary part of the floor at a given height. On encountering the moving part of the floor, which moved in the same direction as their flight, honeybees descended and flew at a lower height. In so doing, bees gradually restored their ventral optic flow (OF) to a similar value to that they had perceived when flying over the stationary part of the floor. OF restoration therefore relied on lowering the groundheight rather than increasing the groundspeed. This result can be accounted for by the control system called an optic flow regulator that we proposed in previous studies. This visuo-motor control scheme explains how honeybees can navigate safely along tunnels on the sole basis of OF measurements, without any need to measure either their speed or the clearance from the ground, the roof or the surrounding walls.