Organs of Equilibrium in Flying Insects

Abstract

IN a recent unpublished lecture to the Cambridge Natural History Society on analogies between insects and aeroplanes, Mr. J. W. S. Pringle pointed out that many insects lack inherent stability ; equilibrium during flight being maintained by appropriate displacements of the wings. Their difficulties are greatest when only a single pair of wings is present. It is in such insects (Diptera, in which the forewings alone are functional, and Strepsiptera with functional hindwings only) that the reduced appendages are transformed into halteres. According to the hypothesis of Fraenkel and Pringle¹, the knobbed haltere serves as an organ of equilibrium. Vibrating in one plane it acts as an alternating gyroscope. If the insect is rotated so that the plane of vibration is changed, lateral shearing forces will be set up in the cuticle of the base of the haltere and will be perceived by the campani-form sensilla.