To work out the information flow underlying the honeybee's anti-collision system, we performed a frame-by-frame analysis of the trajectories of individual bees (Apis Mellifera) flying in a wide outdoor flight tunnel. Forward speed Vx and distance D to one of the two walls happen to be proportional to each other, attesting that the angular velocity Vx/D (Optic Flow, OF) of the image of that same wall is held constant. Like the landing bee holding the downward OF constant (Srinivasan et al. 1996), the bee holds either the left or right OF constant. The bee's behaviour is well accounted for by a lateral optic flow regulator scheme. Simulations showed that this scheme can make a (fully actuated) hovercraft automatically adjust its distance to a wall by regulating the OF on one side (Serres et al., IEEE Biorob 2006).