An "aura" invisible to the human eye surrounds some flower petals and acts as a signal for bees, Cambridge scientists have found.
The flowers create the effect, dubbed a "blue halo" by scientists, usingmicroscopic ridges to scatter light.
In tests, artificial surfaces designed to replicate the halo attracted foragingbumblebees searching for nectar.
The light-manipulating magic is due to the messy nature of the petalnanostructures, which consist of ridges and grooves varying greatly in height, width and spacing.
When the Cambridge team examined fossils of some of the earliest plants from this group they found no evidence of halo-producing petal ridges.
But several examples of aura-generating petals were discovered among two major flower groups that emerged during the Cretaceous period around 100 million years ago, when dinosaurs ruled the Earth.
They coincided with the evolution of flower-visiting insects, particularlynectar-lapping bees.
Flower species with halo-making petals include a type ofevening primrose, the daisy Ursinia speciosa, and Hibiscus trionum, known to gardeners as "Venice Mallow" or "Flower-of-an-Hour".
Previous research has shown that many species of bee are drawn to colours in the shorter wavelength violet-blue end of the light spectrum, said the scientists writing in the journal Nature.
Bees have eyes that can see ultraviolet light beyond the range of humanvision.
However, not all flowers are able to produce blue pigments. Thelight-scattering nanostructures provide an alternative way to attractpollinating insects, the scientists believe.
Lead author Dr Edwige Moyroud, from Cambridge University's Department of Plant Sciences, said: "We can't distinguish between a yellow flower with a blue halo and one without - but our study found that bumblebees can."
Even when both surfaces were the same colour - black or yellow - the beeslocated those with blue halos more quickly.
They also used the halos as a signal telling them which flowers contained asugar solution reward.