Summary

The position and orientation of the thorax and head of flying blowflies (Calliphora vicina) was measured using small sensor coils mounted on thorax and head. During flight, roll movements of the thorax are compensated by counter rolls of the head relative to the thorax. The yaw turns of the thorax (thorax saccades) are accompanied by faster saccades of the head, starting later and finishing earlier than the thorax saccades. Blowfly flight can be divided into two sets of episodes: ‘During saccades’, where high angular velocities of up to a few thousand degrees per second are reached both by thorax and head, and ‘Between saccades’, where the thorax and in particular the head are well stabilized in orientation. Between saccades, the angular velocities of the head are approximately two times lower than those of he thorax, and lie mostly in the range of 0-100 °/s for any rotation (yaw, pitch, and roll). These velocities are low enough to keep the visual blur attributable to rotation limited. It is argued that the split in periods where either rotational optic flow dominates (‘During saccades’) or translatory optic flow (‘Between saccades’) is helpful for processing optic flow when signals and neurons are noisy