A transparent wing of a hawkmoth, Cephonodes hylas, has a highly ordered array of nanosized protuberances in its surface. This protuberance array has almost the same morphology as that of the “corneal nipple array”, which is suggested to function as an antireflective device to light, using a scaled model experiment, a theoretical calculation, and a comparative way. For the direct study of the function of this protuberance array, we prepared an artificial wing without protuberances and compared it with an intact one with protuberances. Directly measuring the light reflectance spectra of the intact wing and the artificial one, we demonstrated that the nanocomposite in the Cephopnodes wing decreases the light reflectance by the wing into 29-48% in the broad wavelength range. This anti reflective effect is also showed by the color difference between the wings, coated by gold, with and without protuberances.