Fly vision is a bit like mosaic. Each individual fly has thousands of tiny pictures of the world that they see, which together create a whole image that is visible to them when they’re far away. A compound fly’s eye has a higher density of ommatidia, making the image even clearer.
Scientists believe that flies have a shortcut pathway that allows them to recognize colors. It’s unlikely that flies are the only animals with this pathway, though. It’s also possible that some animals, like mantis shrimp, lack the ability to make comparisons between photoreceptors and rely on shortcut circuits for all of their color vision. Until this pathway is understood, scientists will have to wonder why people see color differently than other animals, or why people enjoy certain colors.
One reason that flies can’t see white is that their eyesight is limited. Insects have only two types of color receptor cells. Their eyesight has been designed to match their needs. While they can’t focus, they can detect other insects and human hands. Their eyesight also allows them to see ultraviolet light, which helps them find food. However, they cannot see red.
This is because they don’t have a single, common lens like humans. Their eyes are made up of many tiny, specialized segments. This allows them to gather more visual data and use it to create mosaic vision. This way, they can sample thousands of identical images at once and see them in different ways.