Autumn is a time of incredible beauty, when the world becomes painted in the red, orange and yelllow palette of falling leaves. But there may be a deeper purpose to these colours, and the red ones in particular. In the eyes of some scientists, they aren’t just decay made 

pretty – they are a tree’s way of communicating with aphids and other insects that would make a meal of it. The message is simple: “I am strong. Don’t try it.”

During winter, trees withdraw the green chlorophyll from their leaves, and textbooks typically say that autumn colours are produced by the pigments that are left behind. That’s certainly true of yellows and oranges, but reds and purples are a different story.

They are