To scrutinize the logics behind the honeybee's lateral anti-collision system, we filmed bees (Apis Mellifera) flying freely through a wide (0.95m) flight tunnel and analysed the trajectory of individual bees frame-by-frame. The central part of one wall of the tunnel was moved steadily to alter the optic flow (OF) unilaterally (figure 1a). Using a narrower tunnel (0.12m wide), Srinivasan et al. [1,2] had shown that bees tend to centre in a tunnel, and when one wall was moved, bees modified their lateral position according to the authors' OF balance hypothesis. In contrast with these results, we observed that bees flying through a wide tunnel do not center systematically and exhibit instead a wall-following behaviour [3,4]. When we moved one wall at a constant speed V w , we observed that the forward speed of the bee with respect to the moving wall (Vx-Vw) and the distance D to this wall were proportional to each other (figure 1b).