Reptiles
Gecko
Gekkota · also called house lizard
A gecko is the lizard that defies gravity. It runs across the ceiling, hangs upside down from a smooth leaf, and sprints up a pane of glass, all on toe pads that grip by physics alone. It is also the noisy one — the only lizard group that chirps, clicks, and, in the tokay, shouts.
Overview
Geckos are the infraorder Gekkota, roughly 1,500 to 2,000 species, found across the warm regions of the world. Most are small, nocturnal, and drab, with vertical pupils and no eyelids — a fixed clear scale covers each eye, which the gecko licks clean. Most eat insects and spiders, hunted at night around lights and on walls.
The feet
The climbing geckos’ toe pads are covered in millions of microscopic hairs that branch into finer tips, and the summed molecular attraction over that vast contact area holds the gecko on glass and upside down. Not all geckos have them — desert and ground species have claws instead.
Rule-breakers
The day geckos of Madagascar switched to daytime life and evolved round pupils and brilliant green colours. And several species, including the mourning gecko, are all-female, cloning themselves, which has let single individuals colonise islands and greenhouses worldwide.
Status
Geckos as a group are Not Evaluated. Most are common and a few are invasive, but many island endemics are threatened by introduced predators, and some are heavily collected for the pet trade and traditional medicine.
Gecko: common questions
How does a gecko stick to walls and ceilings?
Not with suction cups and not with any sticky secretion, but with a dry physical grip. The underside of each toe carries broad pads made of ridges covered in millions of microscopic hairs called setae, and each seta branches at its end into hundreds of tiny spatula-shaped tips. When the gecko presses a foot down, those tips come into contact with the surface at a molecular scale over an enormous total area, and the sum of the very weak attractions between molecules in contact, known as van der Waals forces, is more than enough to support the animal. The grip switches on and off as the gecko rolls its toes down onto the surface and then peels them up, which lets it run quickly across glass or hang from a ceiling.
Do all geckos have sticky feet?
No. The famous toe pads belong to the climbing geckos, which are the ones people usually picture, but many geckos live on the ground in deserts, dunes, and rocky country and have ordinary clawed feet instead, sometimes with fringes of scales that help them run on loose sand. The leopard gecko, a common pet, is one of these ground-dwellers and cannot climb glass. Even among the pad-bearing species the design varies, from broad leaf-shaped pads to narrow strips, and some can retract their claws into the pad and others cannot.
Why do geckos make so much noise?
Because they communicate by sound, which almost no other lizards do. Male geckos use calls to advertise a territory and warn off rivals and to attract females, and some also have distress calls given when seized by a predator. The sounds range from soft clicks and chirps in small species to the tokay gecko's loud, repeated call, audible across a house and sometimes through the night, which has made the tokay both a famous pet and a famous nuisance. The ability probably helped geckos succeed as nocturnal animals, since a call carries in the dark where visual displays would not be seen.
Are house geckos good to have around?
For most people, yes. The common house gecko and its relatives are small, harmless, non-venomous lizards that live on walls, ceilings, and around lights, and their whole diet is insects, so a resident gecko is a free, quiet form of pest control that reduces mosquitoes, moths, cockroaches, and other bugs. The downsides are minor, mainly the small dark droppings they leave on walls and surfaces and, for the tokay, the loud call. If a gecko needs to be moved it can be gently caught and put outside. In some regions introduced house geckos have displaced native gecko species, which is a concern for conservationists but not for a householder.