Preferred viewing directions of bumblebees (Bombus terrestris L.) when learning and approaching their nest site.

Abstract

Many bees and wasps learn about the immediate surroundings of their nest during learning flights, in which they look back towards the nest and acquire visual information that guides their subsequent returns. Visual guidance to the nest is simplified by the insects' tendency to adopt similar viewing directions during learning and return flights. To understand better the factors determining the particular viewing directions that insects choose, we have recorded the learning and return flights of a ground-nesting bumblebee in two visual environments--an enclosed garden with a partly open view between north and west, and a flat roof with a more open panorama. In both places, bees left and returned to an inconspicuous nest hole in the centre of a tabletop, with the hole marked by one or more nearby cylinders. In all experiments, bees adopted similar preferred orientations on their learning and return flights. Bees faced predominantly either north or south, suggesting the existence of two attractors. The bees' selection between attractors seems to be influenced both by the distribution of light, as determined by the shape of the skyline, and by the direction of wind. In the partly enclosed garden with little or no wind, bees tended to face north throughout the day, i.e. towards the pole in the brighter half of their surroundings. When white curtains, which distributed skylight more evenly, were placed around the table, bees faced both north and south. The bees on the roof tended to face south or north when the wind came from a wide arc of directions from the south or north, respectively. We suggest that bees switch facing orientation between north and south as a compromise between maintaining a single viewing direction for efficient view-based navigation and responding to the distribution of light for the easier detection of landmarks seen against the ground or to the direction of the wind for exploiting olfactory cues.