Hairy feet dancing on the ceiling

Will we ever climb rocks without falling like flies walk on walls or ceilings? German researchers who studied flies dancing on the ceiling think so. After using optical sensors to look at flies under microscopes, the researchers say it's possible to help rock climbers and even robot makers to design wall walking machines.

Will we ever climb rocks without falling like flies walk on walls or ceilings? The Society for Experimental Biology briefly reports that German researchers who studied flies dancing on the ceiling think it's doable. After using optical sensors to look at flies under microscopes, the researchers think it's possible to help rock climbers and even robot makers to design wall walking machines. In the mean time, flies face their own locomotion problem: if their feet can stick to a ceiling, it's very difficult to get unstuck.

Here is the introduction of the Society for Experimental Biology news release.

Ever wondered how flies are able to walk on the ceiling without falling off? Scientists at the Max Planck Institute in Stuttgart (Germany) are investigating this James Bond-style ability of insects to hang upside down from a ceiling. In the future such knowledge could lead to the design of tiny machines that mimic this phenomenon of nature.
The team led by Stanislav Gorb used optical sensors to measure the forces applied by each leg of a fly whilst walking freely on a smooth ceiling. They found that the best attachment force occurred when at least one leg from each side of the fly's body was in contact with the surface.

You'll find more details on Gorb's work by reading about his Biological Attachment Devices for Biomimetics project.)

But it's even more interesting to look at "Shoe fly," a story written by Adam Summers, an assistant professor at the University of California, Irvine, for Natural History Magazine, when he says that flies "depend on a system of hairs to hang on" and explains why.

Under the electron microscope you can see that a fly’s foot ends in a soft pad covered with tiny hairs, called tenent setae. Each hair terminates in a delicate spatula that maximizes the contact area of the foot by flattening against the surface on which it stands. Increasing the contact area increases the frictional forces that keep the foot rooted down. Rock climbers, too, try to increase surface area for a better hold by "smearing," or spreading the balls of their feet over rocks.

The micrograph below illustrates Summers's explanations (Credit: Stanislav Gorb and Natural History Magazine).

A fly foot and its sticky hairs

Summers also explains how two physical forces are involved, friction and adhesion. He also raises an important question: how flies solve the problem of being too sticky?

If its feet stuck too well to whatever it landed on, it would have to just stay put and order room service. So how does it get unstuck? Gorb watched hundreds of videotaped detachment events at a slow speed. What he found is that the fly has not one strategy, but four, for freeing up a stuck foot. Pushing the foot away from the body tends to scrunch up the footpads, popping them free. The other options are twisting the pads loose, prying them up with the help of two little claws on the end of the foot, or simply yanking them away from the surface with brute force.

Below you can see the four ways flies are using to detach a foot from a surface (Credit: Stanislav Gorb and Natural History Magazine).

Flies freeing up a stuck foot

So what's next for rock climbers?

Gorb's group is now working on patterning various materials to scale fly feet up to human size. With photolithography and laser drills they etch a mold of tenent-setae look-alikes, then pour in a liquid polymer that solidifies into a flat sheet studded with hundreds of thousands of tiny, flanged columns. These prototypes have a long way to go before any of them is ready for wall walking.

Even if it takes a while, it will be fun one day to become Spiderman -- or Flyman.

Sources: Society for Experimental Biology news release, April 6, 2006; Adam Summers, Natural History Magazine, February 2006; and various web sites

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