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Sticky Feet

© Zany

Have you ever watched a fly walk across the ceiling and wished you could walk up a wall and along the ceiling too? To accomplish this feat, it's probably helpful to have "sticky feet". Many creatures have "sticky feet". Take the gecko. It can cling to smooth surfaces like glass. How do their feet stick? Scientists have extensively studied the gecko and it is amazing what they have found out.

What are geckos or gekkos? According to Microsoft Encarta geckos are small harmless nocturnal lizards found mainly in topical regions. They eat insects and are the only lizard that can make a sound other than hissing. The site Gecko goes on to describe the sound they make as a voice-a feeble click or chirp to a shrill cackle or bark. That might be disturbing if they are running around your house in the middle of the night. The Global Gecko Association (GGA) has pictures of numerous geckos. All pictures are labeled with the Latin name rather then the common name, but don't let that stop you.

Back in June 2000, scientists (K. Autumn and R. Full) came closer to understanding how a gecko clings to the wall. First look at their web site , an update of the original article that was published in Nature. It gives a very readable explanation of what the researchers discovered. Unfortunately, to view online the original article in Nature, one has to pay for it. If you want to look it up the reference is Nature Volume 405 Number 6787 Page 681 - 685 (2000). Then go on to Hanging In There--the gecko's toehold on life , for a slightly more detailed explanation. Lastly, you can check out Autumn's and Full's web page . Scientists have ruled out several other plausible ideas as to how the gecko clings to smooth surfaces. Geckos don't have suction cups on their feet. It is not due to electrostatic attraction. They don't use hooks or claws nor do they secrete any type of glue since there are no glands in or on their feet. Autumn and Full used an electron microscope to look more closely at the gecko's feet (pictures on their web site). The bottom of a gecko's foot looks wave-like. These waves are called lamella. By looking at the lamella with an electron microscope, it was discovered that each lamella was made up of many tiny hairs called setae. Each gecko's foot has approximately half a million setae. The end of each setae is branched and each branch ends in a spatula, a flat pad-like structure. It is estimated that each setae has between 100 to 1000 spatula. The spatula is so small it can get right into an object or into every cranny so that atomic forces come into play. It is suggested that the spatula align with the surface at atomic distances so that gecko is using van der Waals forces - the weak attraction that molecules have for one another when they are brought very, very close together- to adhere to a surface. van der Waals forces are weak atomic forces but due to the sheer number of spatula (billions per gecko) the combined overall effect of all individual weak forces results in a very strong force. Just as an aside, it is interesting that the one article comments that engineering a foot such as the gecko's is probably beyond human technology.

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