Short Communications How Honey-Bees Know Their Distance From A Near-By Visual Landmark

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Abstract
Insects generally have eyes that are close together and lenses with a very short focal length. In consequence neither stereoscopic nor focus cues can be used to measure the distance of objects that are further than a very few centimetres. To do this insects must rely on information provided by retinal image size or by motion parallax. If an insect knows how large an object appears to be at one distance, it can use image size to compute any other object distance. This method is probably used by some male hoverflies when tracking conspecifics (Collett & Land, 1975). Bulldog ants snap at an image of constant retinal size, and so open their jaws when an appropriately sized prey object comes within range (Via, 1977). The distance of an object can also be specified by the way in which its image travels across the retina or changes size when an insect moves a known distance or at a known speed. To date only stationary locusts have been shown to exploit motion parallax, which they do by performing a specialized side-to-side head and body movement (Wallace, 1959; Collett, 1978). Very little, however, is known about the ways in which freely flying insects measure their distance from stationary objects. We were interested in studying this question in honey-bees because they clearly have a good appreciation of the arrangement of stationary features in their environment, which they will demonstrate all day long as they fly between a food source and their hive. Bees can learn to locate a source of food using near-by landmarks and to do this they must know their distance from such landmarks (Lauer & Lindauer, 1971 ; Anderson, 1977). In this paper we show that honey-bees use both motion parallax and image size or change in image size in determining how far they are from a single landmark.

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