Geckos are lizards belonging to the infraorder Gekkota, found in warm climates throughout the world. They range from 1.6 to 60 cm. Most geckos cannot blink, but they often lick their eyes to keep them clean and moist. They have a fixed lens within each iris that enlarges in darkness.
Geckos are unique among lizards in their vocalizations. They use chirping sounds in social interactions with other geckos. They are the most species-rich group of lizards, with about 1,500 different species worldwide. The New Latin gekko and English "gecko" stem from the Indonesian-Malay gēkoq, which is imitative of the sound the animals make.
All geckos, excluding the Eublepharidae family, lack eyelids and instead have a transparent membrane, which they lick to clean. Nocturnal species have excellent night vision; their eyes are 350 times more sensitive to light than the human eye.
Most gecko species can lose their tails in defense, a process called autotomy. Many species are well known for their specialized toe pads that enable them to climb smooth and vertical surfaces, and even cross indoor ceilings with ease (one hypothesis explains the ability in terms of the van der Waals force). These antics are well-known to people who live in warm regions of the world, where several species of geckos make their home inside human habitations. These species (for example the house gecko) become part of the indoor menagerie and are often welcomed, as they feed on insects, including mosquitoes. Unlike most lizards, geckos are usually nocturnal and are great climbers.