Underneath a Gecko

What am I looking at?

This is the ventral (bottom) side of a fan-fingered gecko (Ptyodactylus guttatus). You can see the small, smooth scales that line its belly, its tail, and the undersides of its legs (1). And look closely at the structure of its feet (2) – they’re well adapted for grasping and climbing, with the pads on the toes (3) providing extra gripping power.

Click on the right arrow to see the top side of this gecko.

Biology in the background

Geckos are known for their broad toe pads and their ability to climb up nearly anything – and even to hang upside down from the ceiling. These toe pads are often thought to be suction cups, but they function in a very different way. As you can see in this image, they are lined with specially adapted scales (called lamellae) that provide increased friction and increased surface area and thus a strong grip.

And frictional adhesion isn’t the only means by which geckos secure their grip. If you could look even closer at the lamellae, you’d see that they’re covered in millions of microscopic hair-like setae, each 10 times smaller than the width of a human hair. The ends of the setae branch and split into even finer spatulae. The setae and spatulae are flexible and thus can conform to microscopic irregularities in any surface. At such a scale, the attractive forces between molecules, called van der Waals forces, become significant. These forces are very weak, but because the combined area of interaction is large, they allow geckos to stick to nearly any surface.

Furthermore, the toes on their back feet are arranged in an asymmetrical pattern designed to give them a better grasp of twigs and branches.

This species of gecko can grow up to 18 centimeters long (about 7 inches).

Technique

These images were created using macrophotography.