- Written by Nadia O'Carroll
In Australia there are 63 native species of gecko, they can be divided into two types – ground dwellers that have slender toes and claws to sprint and burrow; and tree dwellers that have padded toes to climb over smooth surfaces.
The tree dwelling geckos, like the house geckos, perform incredible climbing feats that seem to defy gravity. How can they race up smooth trees at such high speeds, run up glass walls and across ceilings? Was it suction or sticky feet – scientists now know their secret, and the explanation lies in the forces of subatomic physics.
A gecko’s foot is covered with tiny hairs called setae; an individual gecko may have as many as 2 million of them. These setae each branch into hundreds of minute spatula shaped structures, so there may be a billion spatulae on a geckos feet. The researchers were surprised by the strength of the adhesive force in each setae, and they discovered that the adhesion was due to interplay between atoms caused by a phenomena called van de Waals forces. Atoms can be positively or negatively charged, oppositely charged atoms are attracted to each other. Atoms on the gecko’s foot and those on the surface can fleetingly change their charge, and the net effect is that the atoms on the surface are attracted to the atoms on the spatula of the gecko’s toe. The forces are tiny but because there are many hundreds of thousands of points of contact between the atoms of the gecko’s toe and the atoms of the surface, the attachment is strong. If we place our hand against a wall the same process occurs, however because the points of contact between the atoms of our hand and the atoms of the surface are so minimal we don’t experience any attachment to the wall. The only surface a gecko cannot climb is Teflon, because this material was specifically developed to resist van de Waals forces.
Because the attachment between its foot and the surface is so strong (an average gecko with all setae engaged could suspend 133 kg), the gecko cannot just pull its feet away from the surface, it has to peel its feet back from the tips so the seta reach an angle of 30 degrees and this breaks the attachment and allows its foot to detach from the surface.
If a gecko had dirty feet it would interfere with the seta and spatulas’ connection to the climbing surface, scientists found that the spatulas always remain clean and any clogging particles fall off within a few steps.
Another trait of some species of gecko is that they are parthenogenetic ie females can fertilise their own eggs and can lay fertile eggs without any contact with a male gecko. The daughters of these female geckos are not clones of their mothers but are genetically very similar. In the case of the mourning gecko males are unknown.
Scientists believe the geckos climbing attributes could inspire new technology but have remained pretty quiet about the parthenogenesis.