Why are morpho blue?

Abstract

Their large size and the often brilliant blue of their wings put butterflies from the Morpho genus among some of the most spectacular insects in South America. Often mentioned in the reports of explorers in the 19th Century, they have been prominent in curiosity cabinets and natural history displays and are still today the subject of much commerce. We would logically expect the biology of such sought-after species to be well known and understood, but this is not the case. Understanding of the origins and evolution of the iridescent blue color in particular is very limited. Why are Morpho (often) blue?.