Horse Chestnut Traffic Signals

Newly-opened horse chestnut flowers have a yellow spot on the petals, that turns red once the flower is pollinated. More than half the flowers in this photograph seem to have been pollinated, probably by bees seeking nectar that apparently contains a high concentration of sugar in horse chestnut. I recall reading somewhere that this floral colour change is the tree’s way of telling bees not to waste their time visiting flowers that have already been visited and pollinated. The theory was that this works because bee eyes can see yellow but are well known to be relatively insensitive to the longer-wavelength red end of the spectrum. So this is horse chestnut’s traffic light signalling system – conspicuous yellow for ‘proceed’ and inconspicuous red for ‘don’t bother’. I’ve never see any published scientific evidence to back up this plausible but possibly apocryphal story, but with the aid of a decent pair of binoculars it shouldn’t be difficult to see whether the bees do visit the red flowers......