Data from: Gravity and active acceleration limit the ability of killer flies (Coenosia attenuata) to steer towards prey when attacking from above

Female killer flies (Coenosia attenuata) were taken from a laboratory colony, established from animals collected in Almeria (Spain). The colony was kept at 60-70% humidity and a 20-25°C temperature in a 12/12 hour light/dark cycle, and was fed live fruit flies (Drosophila melanogaster). Killer flies were individually placed in transparent vials with only wet filter paper provided for two to three days before testing, to ensure the animals were motivated to hunt. After isolation, two flies were tested in the arena at a time, at room temperature of 20-22°C. The arena was a transparent 160 x 160 x 300 mm box made of 4 mm wide acrylic boards (Perspex®, Mitsubishi Chemical Lucite Group Ltd, Tokyo, Japan), placed with the long axis resting on a white table. The arena was illuminated with two artificial light sources (4Long-Studio, VelvetLight, Barcelona, Spain) each producing an output of 14,000 lx at 1m, comparable to peak light levels of a moderately cloudy day. After placing the flies in the arena, a target was moved along the longitudinal dimension of the box, perpendicular to gravity, in either direction. The target was a black 2.1 mm bead, moved between 0.65 and 0.8 m/s on a transparent 0.15 mm thick fluorocarbon fishing line (Vanish, Berkley Fishing, IA, U.S.A.). The line ran along pulleys fixed at the corners of a transparent acrylic support and was moved by a 23HS-108 MK.2 stepper motor controlled through computer software by a ST5-Q-NN DC motor controller (Applied Motion Products, Watsonville, CA, U.S.A.). The target always started moving outside the box. Flies were tested on repeated trials until they stopped responding to the target. We used two time-synced SA2 Photron cameras (Photron Ltd., Tokyo, Japan) for filming. The recording frame rate used to digitise trajectories was 1000 frames/second, whilst the frame rate to extract wingbeat frequency was 2500 frames/second. The system was calibrated using an altered version of the J.Y. Boguet's Laboratory's MATLAB toolbox (Caltech, http://www.vision.caltech.edu/bouguetj/calib_doc/), running on MATLAB R2014a (version 8.3, MathWorks Inc., Natick, MA, U.S.A.). The movements of the killer flies and target were digitised offline using custom MATLAB scripts for supervised automatic tracking, and smoothed through a fitting algorithm combining trajectory generation using linear fitting with jerk minimisation, run on MATLAB R2012a (version 7.14).