Page last updated at 09:36 GMT, Friday, 15 May 2009 10:36 UK

Velcro petals help bees hang on

By Victoria Gill
Science reporter, BBC News

Bee on snapdragon (Don Manning)
Hanging on is easy with a velcro-like grip

Have you ever marvelled at how a stalwart little bee clings on to a flower during a howling gale?

Researchers have now found the answer, and discovered that flowers have evolved to help it.

A team at the University of Cambridge has found that tiny conical structures on the surface of petals give bees something to grab and hold on to.

The study, published in the journal Current Biology, also found that bees prefer these easy-to-grip petals.

Most insect-pollinated flowers have cone-shaped surface cells, while many others have flat surfaces. So it has long been speculated that the conical "bumps" exist to attract pollinators.

But Beverley Glover and her team are the first to show exactly how they help their six-legged friends.

"These cells also change the colour of the flower by focusing light onto pigments, so researchers thought that might be their purpose," said Dr Glover.

Petal cells
Conical cells (left) make for a easy to grip surface compared to flat cells

"But we've shown, in previous tests, that although they see this colour change, they don't care about it. It's like choosing between different coloured smarties - you can see the difference, but you still eat them all."

So Dr Glover's team set out to discover if the bees could feel these structures through their feet.

First they tested the bees' sense of touch, to see if the insects could distinguish between petals with flat cells and those with conical cells.

They used two types of snapdragon flower, with the same colour of petals and the same scent, but one with a surface covered in these vital bumps and the other with a flat surface.

Each of the flowers was put on top of a small container of liquid.

"The bees get a reward of sweet sucrose solution if they land on the right petal, and a 'punishment' - bitter quinine, which they don't like the taste of - if they chose the wrong flower," said Dr Glover.

And the bees soon learned to discriminate. "If they land on the wrong flower, they feel it through their feet and go 'uh-oh, this feels wrong, I'm not going to stick my tongue in there'," Dr Glover illustrated.

Holding on

To be sure that bees can choose a flower based on the feel of its petals alone, the team tested another group of bees with artificial epoxy resin flowers.

These copies mimicked the two different surface structures of real flowers almost exactly.

Bee on epoxy flower (Beverley Glover)
Flat 'dinner plates' are less of a challenge for the bees

These transparent discs were all the same size and scent. But in this test, each identical fake flower, regardless of its surface structure, contained a sweet reward of sucrose.

The scientists saw that, if these flower-discs were set at a tricky upright angle, the bees much preferred to land on the ones with conical surface cells.

"If the flowers are presented to them flat like dinner plates, they couldn't care less [which type they land on], but if they're upright like lollipops, then they choose the ones that are easier to grip," said Dr Glover.

"We also saw that, on the conical cells, all six of the bee's legs are able to get a grip, and they can rest and turn off their wings."

The bees have minuscule claws on each of their feet that allow them to grab on to the cells.

"With the flat cells, their middle legs are scrabbling continuously, so they keep their wings moving to maintain their balance, which is a lot less energy-efficient," Dr Glover continued.

"It can't be easy to land on a flower - especially in the wind and rain, and the beauty of this is that evolution has come up with such a lovely, simple solution."

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