During locomotion, animals employ visual and mechanical cues in

order to establish the orientation of their head, which reflects the

orientation of the visual coordinate system. However, in certain

situations, contradictory cues may suggest different orientations

relative to the environment. We recorded blowflies walking on a

horizontal or tilted surface surrounded by visual cues suggesting a

variety of orientations.We found that the different orientations relative

to gravity of visual cues and walking surface were integrated, with the

orientation of the surface being the major contributor to head

orientation, while visual cues and gravity also play an important

role. In contrast, visual cues did not affect body orientation much. Cue

integration was modeled as the weighted sum of orientations

suggested by the different cues. Our model suggests that in the

case of lacking visual cues, more weight is given to gravity.