14 Jan 2009
Will Spiderman become
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
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
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
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
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