Geckos are the most specious lizard family, with 1,500 distinct kinds. Geckos are typically small (ranging from 1.6–60 cm), with soft skin. They have adapted to a range of biomes, from deserts to jungles. Most live in warm climes.
Gecko vocalizations are unique among lizards. They talk to one another with clicking or chirping sounds which differ by species.
Almost all geckos lack eyelids, which are compensated for with tough corneas. Geckos lick their eyes to keep them clean.
Gecko adhesion is highly dependent on surface wettability and the presence of water or air between the toe pad and the contact surface. ~ American zoologist Alyssa Stark
Some 60% of geckos can walk up walls and on ceilings, even glass. Gecko soles have ridges (lamellae) that can become adhesive at will. The ridges of each foot have half a million hairs (setae). The end of each hair splits into 100 to 1,000 tiny spatulas which can only be seen using an electron microscope.
Surface contact with the setae spatulas creates billions of fragile molecular attractions, called van der Waals interactions, after Dutch theoretical physicist Johannes Diderik van der Waals. The van der Waals force may be attractive or repulsive. It emanates from molecular dipole moments.
van der Waals interaction is relatively weak compared to other chemical bonding, such as covalent bonding or electrostatic ionic interaction. van der Waals intermolecular attraction depends on the relative orientations of the molecules involved.
Electrostatic forces also effect gecko adhesion, but not as a dominant force. Geckos can adhere to surfaces where electric charges do not accumulate, such as bare steel.
Geckos have complete control over their van der Waals soles. At a certain angle, the subtle attraction is lost, the spatulas detach and roll up like a party favor.
Organic fats (phospholipids) secreted on the feet protect the delicate hairs and provide liquidity that assists adhesion and its release. Geckos can clean their feet of debris by hyperextending their toes.
Namibian Desert Gecko
Bradfield’s geckos live on the coast of Namibia, where cool winds and fog are the norm. Unlike most desert geckos, which are nocturnal, these Namibian geckos are diurnal. Their specially adapted scales efficiently soak up the Sun’s rays and keep the geckos warm.
Bradfield’s Namib day geckos need only 1/4th as much energy as other desert geckos. Slackers to the max, they move leisurely and eat extraordinarily little. Further, these desert geckos need little to drink, as 70% of their water intake is absorbed through their skin from the thick morning fog.
Adults chirp at a high pitch when approaching each other, as statements of claimed territory and other information.