The gecko is a small lizard capable of effortlessly navigating smooth vertical surfaces and even walking upside down on ceilings. This remarkable ability to defy gravity is thanks to a specialized foot structure that engages with surfaces at a molecular level. Most geckos possess five toes on each of their four limbs, giving them a total of 20 digits, though their grip lies not in the count, but in the microscopic engineering of their feet.
Counting and Structure of Gecko Toes
The typical gecko has five digits, or toes, on each foot, similar to many other land vertebrates. These toes are usually broad and flattened, ending in a pad-like structure that is the source of their adhesive power. The underside of each toe pad is covered with a series of parallel ridges.
These ridges are known as lamellae, specialized folds of skin made of keratin, the same protein found in human hair and nails. The lamellae act as a compliant, load-bearing surface and significantly increase the area available to make contact with a substrate. The lamellae are simply the foundation from which microscopic structures emerge to create the lizard’s grip, though they are not the actual sticking mechanism itself.
How Geckos Defy Gravity
The gecko’s adhesion mechanism operates on a scale far smaller than the visible lamellae, involving millions of hair-like structures called setae projecting from them. Each seta is extremely fine, measuring about 5 micrometers in diameter, which is much thinner than a human hair. A single gecko toe can contain hundreds of thousands of these setae, with some species having around 200,000 per toe.
To maximize contact, each seta branches out at its tip into hundreds of smaller, flattened ends called spatulae, which are nanoscale structures only about 200 nanometers across. This proliferation of contact points—reaching up to billions of spatulae across a single gecko—allows the animal to generate a powerful collective force. The spatulae make such close contact with a surface that they engage van der Waals forces, which are weak, short-range intermolecular attractions arising from temporary fluctuations in electron distribution.
While individually weak, the cumulative effect of billions of these forces simultaneously across the foot pad is enough to support the gecko’s entire body weight, even allowing it to hang from a single toe. This is known as “dry adhesion” because it works without any liquid or chemical secretion on a wide variety of surfaces. The gecko controls this adhesive force through a mechanical process of attachment and detachment. Adhesion is engaged by pressing the toes down and applying a slight drag or shear force, bringing the spatulae into optimal contact. To release the grip, the gecko simply changes the angle of its toes, peeling them away from the surface much like removing tape from one edge, which minimizes the required detachment force.
Specialized Feet and Adaptations
While the sticky toe pad is the most recognized feature, not all geckos have this specialized adhesive system; approximately 40% of the over 1,450 gecko species lack the extensive pads. The sticky toe has evolved multiple times, demonstrating a successful adaptation to arboreal or vertical habitats. Conversely, the adhesive structures have been lost in species that adapted to environments where the pads would be a hindrance.
For example, geckos that primarily live on sandy ground, such as dune geckos, often have feet with specialized fringe-like scales. These scales increase the foot’s surface area, preventing the lizard from sinking into loose sand, prioritizing running over climbing. Some geckos have evolved to be completely legless, like the pygopods, which resemble small snakes and are adapted for burrowing. For these terrestrial species, the complex, adhesive lamellae and setae have been reduced or eliminated, demonstrating that the toe structure is highly adaptable based on the gecko’s habitat.