Some flowers have found a nifty way to get the blues.
They create a blue halo, apparently to attract the bees they need for pollination, scientists reported on Wednesday.
Bees are drawn to the colour blue, but it's hard for flowers to make that colour in their petals.
Instead, some flowers use a trick of physics. They produce a blue halo when sunlight strikes a series of tiny ridges in their thin waxy surfaces. The ridges alter how the light bounces back, which affects the colour that one sees.
The halos appear over pigmented areas of a flower, and people can see them over darkly coloured areas if they look from certain angles.
The halo trick is uncommon among flowers. But many tulip species, along with some kinds of daisy and peony, are among those that can do it, said Edwige Moyroud of Cambridge University in England.
In a study published on Wednesday by the journal Nature, Moyroud and others analyse the flower surfaces and used artificial flowers to show that bumblebees can see the halos.
An accompanying commentary said the paper shows how flowers that aren't blue can still use that colour to attract bees.
Further work should see whether the halo also attracts other insects, wrote Dimitri Deheyn of the Scripps Institution of Oceanography in La Jolla, California.
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