This close-up photo of a Calliphora hilli blowfly shows facial features that are common to all insects: compound eyes and two antennae (the latter are difficult to see, as many true flies have short antennae which reduces drag). Most insects, except some species of cave crickets, are able to perceive light and dark. Many species have acute vision capable of detecting minute movement, and many are able to detect light in the infrared, ultraviolet and the visible light wavelengths.Photo: JJ Harrison