Geckos are small to average sized lizards belonging to the family Gekkonidae, found in warm climates throughout the world. Geckos are unique among lizards in their vocalizations, making chirping sounds in social interactions with other geckos. An estimated 2,000 different species of geckos exist worldwide, with many likely yet to be discovered. The name stems from the Indonesian/Javanese word Tokek, inspired by the sound these animals make. The Malay word for gecko is cicak.
All geckos, excluding the Eublepharinae family, have no eyelids and instead have a transparent membrane which they lick to clean. Many species will, in defense, expel a foul-smelling material and feces onto their aggressors. There are also many species that will drop 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 (it is believed that the van der Waals force may contribute to this capability). 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 welcome guests, as they feed on insects, including mosquitoes.
The largest species, Delcourt's gecko, is only known from a single, stuffed specimen found in the basement of a museum in Marseille, France. This gecko was 60 cm long and it was native to New Zealand. It was probably wiped out along with much of the native fauna of these islands at the end of the 19th century, when new predators were introduced there. The smallest gecko, the Jaragua Sphaero, is a mere 16 mm long and was discovered in 2001 on a small island off the coast of the Dominican Republic.
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