We all enjoy the view as autumn leaves change colour, but why does it happen? The late William Hamilton, a biologist at the University of Oxford, suggested that the colour change was a warning – a signal to parasitic pests of a toxic chemical arsenal. After all, the tree actively synthesises anthocyanins, the red molecules in autumn leaves. Why go to all that trouble? If Hamilton was right, insects like aphids, whose eggs laid in autumn become leaf-muching larvae in spring, should steer clear of toxin-rich trees.
His initial study showed that insects do apparently prefer to feed on green rather…
