The More, the Better? A Butterfly with 15 Kinds of Light Sensors in Its Eye

Colors are everywhere in nature, and they communicate useful information. Flowers use colors to advertise that they have nectar, fruits change color when they are ripe, and birds and butterflies use their colorful wings to find mates or to startle enemies. To use this information, animals must be able to see colors. Humans have “trichromatic” color vision, meaning that all the colors we perceive can be produced by mixing three primary colors—red, green, and blue. This is because we have three kinds of light-sensing cells in our eyes, one kind sensitive to red, one to green, and one to blue light. Different species have different types of light-sensing cells. Honey bees also have three types, but they have cells that sense ultraviolet light instead of red light. Butterflies typically have 6 or more types of light-sensing cells, but we found one swallowtail species that has at least 15, which is the record among insects. In this article, we discuss how the world might look to a butterfly with such a complex eye.