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Sunday, April 29, 2007

The Secret of How Spiders Walk on Ceilings

A team led by biomechanics expert Andrew Martin from the Institute for Technical Zoology and Bionics in Bremen, Germany, examined the feet of a small jumping spider (Evarcha arcuata) under an electron microscope. The images they obtained revealed sequences of long hairs (setae) under its feet, as in other spiders. The underside of each of these hairs was covered by even finer hairs (setules) with triangular tips.
In order to determine what kind of adhesion forces were involved, the scientists measured the adhesive force between the spider's foot and a small probe, using a method more frequently employed in materials science. The researchers' calculations showed that a spider hanging from the ceiling by contact through approximately 600,000 setules sets up an adhesive force capable of supporting 173 times its own body weight.

Interpreting these results, Martin concluded that the spider adhered to surfaces through van der Waals forces (the electrostatic attraction that emerges between molecules 1/1,000,000 of a millimeter apart). Van der Waals forces are concerned solely with the distance between two bodies and are unaffected by environmental factors. Therefore, the method by which the spider adheres to the wall can be replicated in the production of materials such as paper notes that can stick when wet and spacesuits that can adhere to surfaces in space. (These hairs are not only found on spiders. It emerged from one study performed in 2002 that geckoes also adhere to surfaces using van der Waals forces.)

For a spider to walk on the ceiling is as much a great ability as it is astonishing. Even more surprising is the way this ability depends on 600,000 fine hairs. There are an average of 100,000 hairs on the human head, yet there are six times this number on the sole of the spider's foot, so many times smaller than the human head. The fact that so many minute hairs have been located in such a small area reveals the existence of a marvel of micro-design. It is also striking the way that these hairs are not just anywhere on the spider's body, but on the soles of its feet. The genetic information for the structure of these hairs is in the spider's DNA and the cells in the sole produce the hairs in accordance with this design plan.

It is of course impossible for a spider to have come up with this design itself. No spider can think of applying the van der Waals forces by performing electrostatic measurements in order to walk on ceilings. Neither can it produce hairs on its feet itself. It is clear that all this has been specially designed in the light of a specific purpose. Indeed, the name of the journal in which the study in question was published is an excellent indication of this: Smart Materials and Structures, 19 April, 2004.

The concept of "smart materials" is one by which scientists aiming to resolve difficulties encountered in the industrial arena under inspiration from the design in nature describe the materials they use in the search to develop products with as few problems as possible.[*] The way that scientists setting out with that intent analyze and make use of the spider foot in their research is a clear sign that it contains an intelligent design. Therefore, the spider's ability to walk on ceilings also emerges as the product of a special creation. There is no doubt that it is God, the Lord of the worlds, Who created the spider and bestowed the ability to walk on ceilings on it. God reveals in one verse from the Qur'an:

Allâh has created every moving (living) creature from water. Of them there are some that creep on their bellies, some that walk on two legs, and some that walk on four. Allâh creates what He wills. Verily! Allâh is Able to do all things. (Qur'an, 24:45)

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