Slippery feet remind beetles to bathe

Sunday, November 14, 2010

WASHINGTON - Insects skitter along leaves, logs and the sides of your picnic basket using their adhesive footpads. Now, a new study has revealed just how beetles keep their feet clean and ready to cling.

The research showed that it’s a decrease in friction that tells beetles to groom their dirty feet.

Lead author Stanislav Gorb of Christian Albrecht University of Kiel in Germany said that the findings could have implications for robot designers or engineers looking for novel ways to measure contamination, reports Live Science.

Beetle feet are covered with miniscule hairs called setae. These setae produce fluid that isn’t sticky but helps increase the molecular attraction between the beetle’s foot and a surface, much in the same way that a wet scrap of paper will stick to glass.

Many plants make it their business to disrupt insect setae by excreting tiny wax crystals that dirty the bugs’ feet. For example, carnivorous pitcher plants secrete wax so insects walking along inside them will slip, fall and get trapped for digestion.

Beetles have special comb-like organs on their legs that they use to clean their feet when they get contaminated. The question, Gorb said, was how the bugs know their feet are dirty. Animals have all sorts of sensors, like the touch receptors in human fingers that gather information about tactile sensations, or the receptors in skin that respond to pressure. What the beetles have in their feet was a mystery.

So Gorb and his colleagues wrangled six leaf beetles onto aluminum-and-silicon surfaces nano-engineered to have different levels of roughness. First, they anesthetized the beetles with carbon dioxide

Next, they used a heating tool to place a drop of molten beeswax onto each beetle’s back, affixing a human hair to each exoskeleton. When the beetles woke up, the researchers attached the hair to a device used to measure force. Then they let the beetles walk on the engineered surfaces.

“We use beetles because they are pretty stupid,” Gorb said. “Or just pretty persistent. They just walk, and they always walk in one direction.”ore friction, please

As the beetles walked, the researchers observed how often they tried to groom their feet. As it turned out, those on surfaces that generated fewer friction forces groomed more often. That suggests the beetles have mechanoreceptors, probably in their joints, which translate frictional forces into signals that trigger grooming behavior, Gorb said.

Despite the fact that the relatively slippery, low-friction surfaces only made the beetles’ feet feel dirty - in actuality, their feet stayed clean during the experiment - the insects never stopped grooming.

Their persistence indicates there’s no signal other than friction getting to the beetle’s nervous system to tell them that their feet are actually clean, Gorb said.

The study has been reported in the journal Proceedings of the Royal Society B. (ANI)

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