If you have ever tried to swat a fly, you know that this pesky insect seems to be able to see n all directions. The fly can see any movement you make because it has five eyes—two large eyes and three tiny ones. You can easily see the two big eyes that cover most of the fly’s head.
These big eyes are called “compound eyes,” and are made up of many little facets packed closely together. On top of the fly’s head are three tiny simple eyes, called “ocelli,” arranged n a neat triangle. With its five eyes watching, the fly is usually able to dodge your swatter. – Dick Rogers