Avoiding obstacles while intercepting a moving target: A miniature fly's solution

The miniature robber fly Holcocephala fusca intercepts its targets using a system whose behaviour is approximated by the proportional navigation guidance law. During predatory trials, we challenged Holcocephala's interception performance by placing a large object in its potential flight path. In response, Holcocephala deviated from the path predicted by pure-proportional navigation, but in many cases still eventually contacted the target. We show that such flight deviations can be explained as the output of two competing navigational systems; pure-proportional navigation and a simple obstacle avoidance algorithm. Obstacle avoidance by Holcocephala is here described by a simple feedback loop that uses the visual expansion of the approaching obstacle to mediate the magnitude of the turning-away response. We name the integration of this this steering law with pro-nav "Combined Guidance". The results demonstrate that predatory intent does not operate a monopoly on the fly's steering when attacking a target, and that simple guidance combinations can explain obstacle avoidance during interceptive tasks.

Methods
The enclosed data features the trajectories of Holcocephala fusca intercepting a moving dummy target whilst avoiding a static obstacle. This data was collected under field conditions using time-synchronised Photron Fastcam 2 cameras recording at 1000 frames per second. The data has been converted into 3D trajectories using checker-board calibration of the cameras immediately after capturing interception flights.