Visual Scanning in the Desert Locust Schistocerca Gregaria Forskål

Abstract

1. This paper describes a lateral swaying movement performed by desert locust nymphs. This movement is called ‘peering’. 2. The angle through which the body moves is influenced by the position of objects in the visual field, showing that the movement is related to vision. 3. When given a choice of two objects at different distances the nymphs show a preference for the nearer one. The estimation of the relative distances of the two objects is not achieved by a binocular method nor is it based on the angle subtended by the objects. 4. An experiment is described in which an object is moved while the insect is peering. If the object is moved in the opposite direction to the insect's motion the insect jumps short of the object. This seems to support the hypothesis that one of the functions of peering is to estimate distance by the extent of the movement over the retina of an object's image. 5. This method of distance estimation is discussed with relation to the binocular method. 6. It is suggested that in some cases the peering observed may represent a preliminary scanning of the visual field and may provide information about the finer details of the field.