Beetle: Flowing feet as an adhesive

Why insects can walk on the ceiling

Tiny hairs on the beetle feet flow into contact with surfaces and increase the adhesion. © RUB
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"Flowing" hairs on the feet allow beetles to run on the ceiling. Bochum researchers have now been able to observe this for the first time live using X-ray microscopy. They found that the flat ends of the many thousands of tiny tiny hairs that make up the insect's leg behave like a viscous liquid when in contact with the surface.

This so-called viscoelastic flow increases the effective contact surface and allows a high holding force that exceeds the body weight and holds the animal to the ceiling, the scientists in the current issue of the journal "Journal of Experimental Biology".

An old question

Already Aristotle wondered about the ability of insects to walk on the ceiling. As causes at that time hooks, suckers or sticky liquids were suspected. More recently, systematic investigations have refuted these hypotheses. Rather, it has been shown that an insect foot consists of thousands of fine, micrometre small hairs that adhere to the surface via adhesive forces.

Dividing the contact surface into a large number of individual contacts is an effective principle for achieving high holding forces. For example, a fly has more than 5, 000 adhesive hairs. The heavier the animal, the more numerous and finer are the hairs. So geckos have about 500, 000 finest hairs with dimensions of only 0.2 to 0.5 microns.

A new technique

With previous techniques such as electron microscopy, however, it was not possible to study the fine sticky hairs in fresh contact with the substrate, since the samples had to be dried and examined in a vacuum. display

The physicist Thomas Eimüller from the Ruhr University Bochum, together with the biologist Stanislav Gorb from the Max Plank Institute for Metals Research in Stuttgart, was therefore looking for a new imaging technique. Using an X-ray microscope from the BESSY II synchrotron radiation laboratory in Berlin and the help of the physicist Peter Guttmann working there, they finally managed to study insect hair in fresh contact with a resolution of about 30 nanometers. The insect hairs were brought into contact with a very thin film, which is permeable to X-rays. "This method makes it possible to measure material thicknesses with nanometer precision, " explains Eimüller.

Learn from beetles

The researchers found in the adhesive hairs of flies and beetles before a viscoelastic flow of the hair ends. These increased in contact with the surface like a viscous liquid. The insects thus achieve both an adaptation to the roughness of the surface and a magnification of the effective contact surface. Both increase the holding power. Therefore, to lift the feet, the insects use a gimmick: they probably peel off the panties from the side, as one pulls off a strip of tape.

"We can learn from these tricks that K fer has been using for millions of years, " says Eim ller. The goal of the collaboration with the Stuttgart biologists is the development of polymer adhesive films based on the principles of insect adhesion. The dream of sticking Spiderman on the walls of high-rise buildings is getting a bit closer with the new findings

(idw - Ruhr-University Bochum, 05.06.2008 - DLO)