Geckos at Gecko Villa in rural Thailand, and How Geckos Stick to Walls

Thai schools generally do not teach Latin at school, so we think it is more appropriate to call them Jingjoke of the Ten family, as this is the tutting noise they make when you talk to them and the name of my family.

They like hanging upside down on ceilings to make you jealous, and to make it easier to talk to them when they come out at night and you are in bed. They like to hold parties around lights at night as they wait for dinner to be served in the form of an insect buffet.

They are totally harmless and are good omens when found in houses, generally meaning that wealth will come to the household. We are still hoping to verify this.

The House Gecko is a well-adapted escape artist, managing to get out of the smallest spaces and taking advantage of any loss of concentration. Being so adapt at escaping, it is next to impossible to handle them - especially as their tails come off easily.

The House Gecko: Hemidactylus frenatus of the Gekkonidae family. Colour is variable, changing based on temperature and background. Their distribution is throughout mainland Asia and Southeast Asia, and as far away as south and east Africa and across the Pacific Ocean to Mexico. The house gecko is an anthropophilous species and since the 19th Century it has been inadvertently spread from Asia to many tropical islands and continents.

Geckos scamper across the smoothest surfaces and hang upside down from ceilings. Scientists, lumbering ponderously in pursuit, have spent decades trying to un-stick the adhesive magic of these little lizards. They have not caught up, but have now come the closest yet.

Robert J. Full from the University of California, Berkeley, and colleagues announce that geckos stick to surfaces by tapping into nothing less than the molecular structure of the surfaces they traverse. They stick by a kind of atomic energy.

Gecko feet stick even in a vacuum, so they can't be suction cups; geckos can walk across polished glass, so they can't be getting any physical purchase on the microscopic imperfections of surfaces. Gecko feet stick to surfaces even when the air around is electrically charged, so they can't be exploiting electrostatic attraction to the surface (the kind of force that allows a well-rubbed toy balloon to stick to the ceiling.) Gecko feet do not have gland cells, so they can't be adhering by some kind of secreted glue.

So, a change of perspective was required. Rather than looking at the feet of the gecko, researchers have been looking at the surfaces they cross.

In the 1960s, German Uwe Hiller found that the stickiness of a gecko increased with the 'surface energy' of what the creature was scuttling across. Surface energy is a measure of the 'roughness' of a surface at the atomic scale. A high- energy surface is loosely packed, with a lot of loose atomic bonds hanging around.

Hiller suggested that geckos might be exploiting 'van der Waals forces' -- weak, short-range attractions between atoms of opposite electrical charge. Many of the properties of water, such as its high boiling point, can be explained by van der Waals forces that bind water molecules into loose, short-term associations.

So much for molecules -- could van der Waals forces be strong enough to suspend a macroscopic object, such as a lizard, from a ceiling? It has taken another 30 years for Hiller's amazing idea to be substantiated.

Gecko feet aren't smooth. Each foot is covered in fine hairs, called 'setae' -- about half a million on each foot, or two million per gecko. Each seta ends in a fringe of up to 1,000 sub-microscopic hairs called 'spatulae'. There are billions of these on each gecko, creating a surface of microscopic roughness that, apparently, taps into the energy of surfaces.

Full and his co-workers measured the tiny forces generated when a single seta on the foot of a Tokay gecko (Gekko gecko) comes into contact with a surface, and investigated the geometry of precisely how setae and surfaces interact, as they report in Nature.

The setae tend to point towards the heel. As a gecko takes a step, driving his or her sole into the wall, window or ceiling and pushing it backwards, the setae become maximally engaged. The force on each seta is minuscule, but the cumulative effect is enormous. If all the hairs were simultaneously stuck to the surface, the feet of a gecko could experience an adhesive force equivalent to ten atmospheres.

So how, once stuck, does a gecko remove itself? The animal releases each foot by peeling off the setae, rather as one would adhesive tape.