At Idyllic we try to bring to the attention of browsers interesting Wild Life happenings in Southern Africa

 

 
14 Jan 2009
Roddy Smith
  

                                                                                                                                                                                   
Will Spiderman become a reality?


Geckos are one type of animal that one doesn’t have any trouble finding in the warmer parts of southern Africa. Indeed, more often than not they can be seen without stirring from your bed (or from the bar).

Geckos are lizards belonging to the family Gekkonidae. They are the only lizards that have a voice, and the name is derived from the Indonesian word gekok, which comes from the typical noise some species make.

They also have the best eyesight of any lizards. Theirs is an unblinking stare, since they have no eyelids. Instead, they regard the world through a protective transparent scale, which is cleaned when it gets dirty by licking it with a large fleshy tongue, like a flexible windscreen wiper.

Certain species have specialised adaptations to their environment: desert geckos can run over loose sand with their fringed toes and the arboreal flying geckos of south-east Asia can glide on skin membranes stretched between their limbs.

What most of them have in common, however, is that they are all amazing climbers. They are able to climb up any vertical surface and even run upside-down across the ceiling. They can do this on any type of surface, even glass. Most of us grew up believing that they had some sort of suction cup on their toes. Other theories were that they used capillary action, adhering to moisture in the surface, or that they secreted some sticky substance from their feet. Only very recently has it been discovered that what really happens is more remarkable and more effective than any of those theories.

Geckos have millions of tiny hairs only 0,1 mm long called setae on each toe. Each seta in turn is split up into up to 1 000 even tinier endings called spatulae, only 200 nanometres (0,0002 mm) wide, which is less than the wavelength of visible light. These billions of little hair-endings make it possible for a considerable total surface area to come into very close contact with the climbing surface and adhere to it due to Van der Waal’s forces.

For those who, like I did, have absolutely no idea what Van der Waal’s forces are, they are weak electrodynamic forces that act over short distances and hold molecules together. The actual molecules of the gecko’s foot are thus bonding with those of the surface it is climbing on.

This is incredibly effective — a gecko can hang from a single toe. Indeed, it is about 1 000 times stronger than the gecko actually needs. Researchers calculate that the adhesive effect of a million setae (which some geckos have on one foot) is enough to support the weight of a 20-kilogram child. Not only this, but it works under water, in a vacuum and on practically any known surface.

The setae also detach very easily — when the angle of the seta to the surface is increased, it just comes away. A gecko can do this very easily because its toes are jointed the opposite way to ours. When it flexes them, they bend away from the surface it is walking on rather than towards it.

Not only this, but unlike conventional artificial adhesives (think sticky tape), which become progressively less effective if they are repeatedly used, geckos’ feet do not. This is because any specks of dirt that adhere to them through Van der Waal’s forces are even more likely to stick to the larger and more electrodynamically attractive surface they are walking on, so the feet clean themselves as they walk.

It’s not just their feet. Even more recent research has discovered that the gecko’s tail is pretty useful too. High-speed video footage has revealed that if a gecko does lose its footing, it jams its tail against the surface to stop itself slipping while it regains its grip. If it actually falls, for example from a tree, it uses the tail to turn itself so it lands feet first. Experiments in a vertical wind tunnel show that it can also steer its fall so as to land on a leaf or branch rather than fall all the way to the ground.

Not surprisingly, these discoveries have caused a flurry of research and development activity as commercial companies compete to produce a synthetic version of the gecko’s adhesive: one square metre of a material called “Synthetic Gecko” produced by British Aerospace (BAe) will suspend a family car from the ceiling. Various United States companies and universities are working on climbing robots, which could be used for fire-fighting and rescue, etc.

We could yet see Spiderman becoming a reality, but while they may be able to give him the grip, they’re going to have to come up with something pretty special to match a gecko’s speed across the ceiling.

• Roddy Smith works as a guide and conservationist in the lower Zambezi Valley.

 
 

 

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