Acquisition of stereo images. (a) Pair of synchronized cameras (cr, right camera; cl, left camera, yellow circles) with a resolution of 2352 × 1728 pixels at 60 Hz recording stereo images of a Giant honeybee nest on a balcony of a house in Chitwan, Nepal. Before the measurements, the cameras were fixed to an aluminium carrier rig and calibrated; the orange circle refers the movable dummy wasp (dw; note the black and white stripes) on a cable-car device; tl, trigger light (green circle) for the synchronization of the HD cameras and additional sensory equipment (cf see Additional File 1, Movie S1). The frame grabbers and the computer were located in the adjacent room to the right side. (b) Schematic showing the camera setup at a Giant honeybee nest with a central comb with several layers of worker bees (termed "bee curtain"); numbers indicate distances in metres. (c) HD image of the experimental giant honeybee nest. The white rectangle indicates the area recorded by stereo imaging. The yellow line marks the "mouth zone", which is the most active zone of the nest where bees depart and arrive. (d) Example of a pair (left and right) of stereo images as acquired by the stereo cameras.