New research suggests that there are certain flowers that attract bees with a rather unusual optical illusion that’s visible to the insects, but not to human observers in most cases.

Typically, gardeners attract bumblebees by planting blue flowers such as hydrangeas and delphiniums, as noted on a report from the Daily Mail. These flowers are high in nectar and are easily capable of attracting bees on their own. But the new discovery points to something different altogether — flowers luring the insects with microscopic ridges found on their petals. These ridges spread out a “blue halo” of light, creating an “aura” that could also be used as a bee signal.

“The exciting thing is that it is a new optical trick – we didn’t know that flowers could use disorder to generate a specific color, and that is quite clever,” said study co-author Beverley Glover, from the University of Cambridge in England.

The Guardian wrote that the discovery of how flowers attract bees via optical effects builds on previous research from Glover and her colleagues, who had found that the small ridges on the petals of select flowers are capable of bending light — a phenomenon known as diffracting. Having discovered some plants that could diffract, the researchers examined the petals of 12 different flower species to see if the phenomenon also occurred in them. Using artificial flowers with and without blue halos and testing them on bees, the researchers later found that the bees tended to go to the flowers with halos, while also using the blue hue to inform them which of the artificial flowers came with a sugar solution reward.

Based on their findings, Glover’s team found that each of the flowers’ ridges had their own unique architecture, with the heights and spacings of the ridges tending to vary in particular. And while it was found that all 12 flowers only gave off a weak sheen, the researchers discovered that the ridges were also capable of dispersing blue and ultraviolet light. With that established, the flowers were revealed to have a “blue halo” effect, one that can only be seen by people in darkly-pigmented flowers, and one that differed based on the ridges’ degree of variation in height or spacing.

Humans can’t see the blue hue emitted by the evening primrose’s petal ridges, but bees can. [Image by High Mountain/Shutterstock]

The Daily Mail further noted that flowers that attract bees with the blue halo have been around for millions of years. Fossils of flowering plants, or angiosperms, from over 200 million years ago did not yield any proof of petal ridges capable of such optical illusions. But there were “several” examples of blue halo-generating ridges found in examples from two flower groups that had first appeared about 100 million years ago, during the Cretaceous period. These flowers reportedly existed just as bees and other “flower-visiting insects” were beginning to evolve.

“Our findings suggest the petal ridges that produce ‘blue halos’ evolved many times across different flower lineages, all converging on this optical signal for pollinators,” said Glover.

According to the Daily Mail, the Venice Mallow (Hibiscus trionum), Queen of the Night tulips, a species of daisy (Ursinia speciosa), and a species of evening primrose (Oenothera stricta) are among the examples of blue halo-emitting flowers that attract bees.

[Featured Image by Lucia Speck/Shutterstock