Like most mammals, fruit flies have many body hairs including large coarse hairs and much smaller, fine hairs. Though the hairs on the body of an insect are quite different in structure, they have many of the same functions as mammal body hairs, including insuation and tactile sensation.
Most insects have a pair of relatively large, compound eyes. What most people don't realize is that they
may also have as many as 3 simple eyes, known as ocelli. The ocelli can only distinguish between light
and dark, thus do not deliver an actual image.
The compound eyes, on the other hand, are capable of producing a foucsed image. It is generally accepted that each lens perceives a single pixel, similar to the way a CCD image device works. The insect's brain puts the pixels together to form a complete picture. The covering of the eyes is shed every time the insect moults. This cast off skin looks like an egg crate and is a common component of dust. Compound eyes vary in size from 1 species to another and some insects, such as dragonflies, can see almost 360 degress without turning its head. The size and seperation of the eyes is also subject to sexual dimorphism, it is, for example, very easy to distinguish between male and female mayflies by looking at their eyes.