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Bloomin' marvellous: Flowers generate aura to act as sat nav for bees

Head towards the light - Flower's hidden message for bees Photo: PA images

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, using microscopic ridges to scatter light.

In tests, artificial surfaces designed to replicate the halo attracted foraging bumblebees searching for nectar.

The light-manipulating magic is due to the messy nature of the petal nanostructures, which consist of ridges and grooves varying greatly in height, width and spacing.

Ridges in the petal surface generate the aura Credit: PA Images

"We had always assumed that the disorder we saw in our petal surfaces was just an accidental by-product of life - that flowers couldn't do any better. It came as a real surprise to discover that the disorder itself is what generates the important optical signal that allows bees to find the flowers more effectively."

– Professor Beverley Glover, director of Cambridge University's botanic garden

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, particularly nectar-lapping bees.

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Flower species with halo-making petals include a type of evening 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 human vision.

However, not all flowers are able to produce blue pigments. The light-scattering nanostructures provide an alternative way to attract pollinating 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 bees located those with blue halos more quickly.

They also used the halos as a signal telling them which flowers contained a sugar solution reward.