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.

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.

The obstacle (termed "bar") took the form of a flat sheet of painted black acetate. 'Thick' and 'Thin' in the bar descriptor refers to either a 5 cm width or 2.5 cm width, as detailed within the manuscript. A ReadMe file is included that details each of the files within each data folder, and what they tell you. Separately, there is an example plotting script which should demonstrate the use of all the included data to reproduce figures similar to those in the manuscript.