Head Movement of Flies during Visually Guided Flight

Abstract

MOST visually advanced animals are able to move their eyes relative to the body. This makes vision independent of body movements; in man it enables the eyes to keep the visual world stationary on the retinae, to scan the field of view, and to maintain fixation on moving objects¹. The extent to which animals other than vertebrates are able to perform these activities is largely unknown; many, especially arthropods, make body movements tending either to stabilize the visual surroundings^2,3 or to cause fixation of objects by the eyes^4,5. In a very few cases, however, it has been shown that arthropod eyes may make directed movements independent of the body: examples are the fixation of prey by mantids⁶ and by salticid spiders⁷, and compensatory eye movements in a moving visual surround by crabs⁸ and locusts⁹. Here I describe the head movements (and therefore, in insects, eye movements) made by blowflies during sustained flight. I show these to be of two kinds: rapid saccadic flicks in which the head takes up a new angle with respect to the visual surroundings, and stabilization movements which keep the angular position of the head almost constant, in spite of body movements of up to 10° in either direction.