Fig. 1. Design of (A) training and (B) testing set-up. (A) For training, beetles were kept in constant humidity for 24 h, being exposed to a directional light emanating from one of four geographic directions. The light in training came from a frosted light bulb and passed through a diffuser of white paper. (B) For testing, beetles were placed in the centre of the arena under a plastic Petri dish. They were released by raising the Petri dish after a delay of 2 min, and their movement was observed by a camera located underneath the arena. Both training and testing took place in the same location in the laboratory.