Stacked macrophotograph of a wasp (Ophion luteus) head with compound eyes, one of three ocelli and mouth parts. O. luteus is a widespread european nocturnal ichneumonid wasp. The surface of the compound eyes is a tight arrangement of hexagons, which cover the light-sensing structure, the ommatidium. The three ocelli, considered to be far more sensitive to light than the compound eyes, are thought to assist in maintaining flight stability.