GECKOS
Geckos are soft bodied lizards that can reach lengths of about 18 centimeters and have the unique ability to walk on almost any surface at any angle, even upsidedown. They are usually brown or grey in color and have patterns of speckles on their backs. Most geckos are nocturnal and operate at lower body temperatures than diurnal lizards.
Geckos are familiar to travelers to tropical regions. They hang out at night around lights on the walls and ceilings in restaurants and hotel rooms in jungles, beach areas, islands and deserts around the world. There are about 1,000 different species of gecko. Only a few live in colder climates. Their name is derived from clicking "gecko" sound they make.
Most geckos are carnivorous. They feed on insects like moths and winged termites and like to hang around light sources that attract insects. They sometimes fight among one another for the best positions around the light. Some geckos consumer nectar, pollen and fruit. A few species eat prey as large as mall mammals and birds. Females often feed side by side while males fight off intruders that approach their territory. Geckos are fed upon by mongooses, cats, and birds. Sometimes thy are eaten by giant centipedes.
Tokay geckos are notoriously noisy creatures that make loud calls. Other geckos are even noisier. Laura Geggel wrote in Live Science: If the giant leaf-tailed gecko (Uroplatus fimbriatus) feels threatened, it will make sure you do, too. When this gecko is disturbed, it opens its jaws wide, flashing its bright red mouth and tongue before it releases a piercing distress call that sounds just like a child's scream, Smithsonian's National Zoo reports. [Source Laura Geggel, Live Science, July 11, 2024]
Some Chinese medicine users believe dried geckos can help treat asthma, diabetes, skin disorders and other ailments. According to mongabay.com: “Millions of tokay geckos continue to be traded for traditional medicine, despite waning belief that the colorful lizards are a cure for AIDS, reports a study from TRAFFIC. The study found that a spike in tokay gecko demand due to rumors that it could cure HIV/AIDS was relatively short-lived, lasting from 2009 and early 2011. Nonetheless geckos are still traded in large numbers, with over-collection impacting wild populations across much of the reptile's range, especially in Thailand and Java. The study notes that Taiwan has declared imports of at least 15 million geckos since 2004. Major consuming nations also include mainland China, Hong Kong, Taiwan and Viet Nam. [Source: mongabay.com, April 12, 2013]
See Separate Articles: REPTILES factsanddetails.com ; LIZARDS factsanddetails.com
Websites and Resources on Reptiles: Reptile Database reptile-database.org ; Reptileweb reptilesweb.com ; Reptile Phylogeny whozoo.org/herps/herpphylogeny ; Geckos Global Gecko Association gekkota.com ; Leopard Gecko Guide leopardgeckoguide.com ;Gecko and Lizard Photos mongabay.com ; Websites and Resources on Animals: Animal Diversity Web animaldiversity.org ; BBC Earth bbcearth.com; A-Z-Animals.com a-z-animals.com; Live Science Animals livescience.com; Animal Info animalinfo.org ; Encyclopedia of Life eol.org , a project to create an online reference source for every species; World Wildlife Fund (WWF) worldwildlife.org the world’s largest independent conservation body; National Geographic National Geographic ; ; Endangered Animals (IUCN Red List of Threatened Species) iucnredlist.org ; Biodiversity Heritage Library biodiversitylibrary.org
Gecko Characteristics
Geckos have a large head. Nocturnal species see with slit- or elliptical-shaped pupils that work well in the dark. Scientists can find geckos easily at night by shining flashlights which illuminate the gecko’s eyes. Diurnal geckos have large bulging eyes and round pupils.
Almost all gecko species lack eyelids and unable to close their eyes. Like snakes they have transparent scales over their eyes that offer protection and are periodically shed. The tongues serves as a windshield wiper, keeping the eyes clean. Many desert species lick their eyes to remove windblown material and lick their heads to collect dew that has condensed on their skin.
Gecko tails contain fat the geckos can use if food supplies run low. When attacked by bird or a tree snake a gecko can grow back its. If the tail is split two tails may grow. In Australia a gecko was found with five tails and it was concluded that its tail had been split five ways.
Geckos have a good sense of smell. They pick up pheromones of the geckos and can discriminate between different prey on the basis of chemical signals.
Geckos can shed their tails like other kinds of lizards. Special cells at the base of their tail contract so no blood is lost. The tail contains bone and nerves but does receive signals from the brain. After it comes off it jumps and twitch until it "dies." By that time the gecko has had ample time to make an escape.
Gecko Walk on Walls and Ceilings
Most species of geckos are as comfortable scampering across walls, ceilings and even windows as the are running on the ground. They can run across ceilings at speeds up to three feet a second ; hold the weight of their entire body with one toe; cling upside down on window panes; and never lose their grip even if he scamper through dirt. What is more, they do all this without using any kind of adhesive or suction cups.
Geckos can jump from tree to tree by catching a leaf on the second tree with one toe. Some desert geckos have fringes of scales on their feet that prevent them from sinking in the sand. The Vaseline-like chemical fluon can applied to surfaces to make geckos fall off.
Gecko feet come in an amazing variety. They are not sticky but dry and smooth to the touch. It was long thought that gecko feet splayed out and had little claws and they moved on vertical and upside down surfaces similar to way cockroaches do by wedging parts of their feet their into minute cracks and using some sort of suction devise. But this is not the case.
Gecko Feet Adhesion
Geckos employ a method called contact splitting. Their feet have millions ultrafine fine hairs and hair tips that temporarily rearrange electrons on the walking surface, creating an electrodynamic attraction.
Gecko toes are lined with plates that are covered with hairs called setae that branch into hundreds of spatula-shaped microhairs. There are about 500,000 nano-size bristles on each of the gecko’s four feet. Each bristle is split into 100 to 1,000 spatula-shaped mini-bristles, hairs or filaments. This works out to two billion filament be square centimeter and 6.5 million on each toe. Each filament is only a hundred nanometer thick and are so small they interact in the molecular level with the surface in which the gecko walks.
In the nanoworld of the microhairs a faint intermolecular attraction called the van der Waals force pulls objects together. Multiplied millions of times this force creates enough adhesion that holds the feet of a gecko to surface of glass.
The geckos’ unique adhesive ability was discovered by the Gecko Team led by Kellar Autumn of Lewis and Clark College and Robert Full of Berkeley. For a more detailed description on gecko adhesion see The Gecko’s Foot by Peter Forbes (W.W, Morton, 2006)
Van der Waals Force
Van de Waals force used gecko feet adhesion is not gravity, electricity, or magnetism, nor is it chemical attraction. It is an adhesive force of quantum physics caused by an interaction between the positive and negative charges of different atoms that cling together briefly as their electron clouds share electric charges.
Van der Waals force is generated by molecules’s fleeting positive and negative charges, which pull any two adjacent objects together. It can be felt in spaces no larger than two nanometers (billionths of a meter). It works on the molecules on whatever surface the gecko is walking on and doesn’t require any special chemistry and theocratically could be applied to any material
Van der Waals force works between the atoms on gecko's feet and the atoms on the surface it is climbing or hanging on to because there are so many setae and microhairs on gecko feet allows so many atoms to interact with the surface. The force created by one gecko is enough to lift 127 kilograms. There is Van der Waals force between a person's hand and a wall but it is relatively weak because not so many atoms on the hand and surface come in contact.
Physics Behind Gecko Movement
Geckos walk in such a way that their micro hairs roll on the surface and release as easily as they cling. If a gecko’s feet were covered with suction cups, a great deal of energy would be required to break the bond when a gecko lifted its foot. Instead, geckos change the angle of their setae and this allows them easily lift their feet.
But adhesion is only part of the process. For a gecko to scamper around on walls and ceilings---which it can do at speeds up to 1 meter per second---it has to be able to unstick its feet quickly and effortlessly. Scientists that have studied this---namely biologists Bob Full and Kellar Autumn---found that gecko adhesion is highly directional. If the toes are pushed forward they stick if the are pulled into the opposite direction they release.
What make feet function so well is not just the nano hairs but the way those hairs grow on large hairs and then in turn grow on toe ridges which are part of bigger toe parts, creating a seven part hierarchy that give the gecko all the capabilities it has.
The setae are also believed to be to be behind the fact that geckos are extraordinary clean even though they never groom themselves. Even if they are immersed in the most god awful dirt and grim geckos will shed whatever is covering them in few quick steps. Setae repel dirt even when it is isolated from the gecko. Autumn’s team calculated that a particle of dirt is too small to be attracted by Van de Waals force and the setae are too close for the dirt to penetrate and are thus quickly repelled.
Geckos do fall or slip from time to time. When this happens their tail plays an important role in correcting mistakes. When a gecko is climbing a vertical wall and starts to slip the tail arches and its tip pushes against the wall surface, which usually prevents the head and the upper body from pitching back, away from the wall . If it doesn’t , then most of the tail flattens against the wall. These movements, researchers say, stop the gecko from within a quarter of a second. When geckos fall they always land right-side-up like a cat. But unlike most other animals that right themselves by twisting their spine, geckos right themselves by swinging their tails around when the are upside down, to produce a counter-rotation that takes about a tenth of a second.
Gecko Robots and Uses of Gecko Adhesion
Scientists led by Mark Cutkosky of Stanford University have created a robot called Stickybot that can climb up walls like a gecko. The robot weighs 500 grams and has pads on it feet made of a urethane fabric with tiny bristles that end in 30-micrometers points. These are not as flexible and adherent as a real gecko’s but the robot does stick to a wall. At this stage of the game---despite the use of high tech sensor and actuators and space age polymers to make it flexible and stiff and branching tendons to distributed weight evenly like on a real gecko---the robot is very slow but designers hope to speed it up and use it in search and rescue missions and other uses.
This gluelike effect of gecko adhesion can have innumerable uses. Scientists are using geckos as a model to make better adhesive tapes that will work in outer space and vacuums. The stickiness of ordinary adhesive tapes is caused in part by tiny bubbles of trapped air, which are not existent in space or a vacuum. Scientists are also studying the process to adapt it to an adhesive tape that can be used over and over; fumble-free football gloves; robotic rovers that can move quickly over the Martian surface; Spiderman-like climb equipment and material that can replace the screw.
Gecko Behavior
Many geckos are arboreal (live mainly in trees), nocturnal (active at night), motile (move around as opposed to being stationary), sedentary (remain in the same area) and territorial (defend an area within the home range). Home ranges and territories tend to be quite small, perhaps encompassing just one wall of a building or part of a tree. Males can be quite aggressive defending their territories against potential competitors and are regarded as more aggressive than other gecko species. It is not uncommon for them to approach and bite other geckos, which may lead to tail loss or scars.
Geckos communicate with vision, touch and sound and sense using vision, touch, sound and vibrations. Most lizards make few vocal sounds other than hisses. In contrast geckos make a wide a variety of sounds including coughs, clucks and barks. When they bark they move their heads up and down. When threatened some geckos "scream" loudly in an attempt to startle their attacker long enough to make an escape.
Fighting geckos arch their backs make clicking and growling noises, turn side to side and then clamp their jaws onto each other’s head or body and wrestle from that position. Sometimes the dominant combatant dangles the loser over the ground. Sometimes they both fall to the ground.
Geckos’ Mysterious 'Sixth Sense'
In October 2024, scientists announced that they had now discovered that geckos have hidden “sixth sense” that lets them pick up low, runbling vibrations. Michael Irving wrote in ScienceAlert: Like other lizards, tokay geckos (Gekko gecko) have hearing that's specialized towards higher frequency sounds — they're most sensitive between 1,600 and 2,000 Hertz, but can hear beyond 5,000 Hertz. That's just using their regular old ears, though. Two researchers at the University of Maryland found that tokay geckos can also use a different structure, not normally associated with hearing, to sense much lower frequency vibrations, in the range of 50 to 200 Hertz. The research was published in the journal Cell Reports.[Source Michael Irving, ScienceAlert, October 11, 2024]
The saccule is a part of the inner ear that plays a key role in balance and keeping track of head and body positioning. This structure is conserved across fish, amphibians, reptiles, birds, and mammals, but only the first two were known to use it for hearing. Now, it seems at least some reptiles can too. "The ear, as we know it, hears airborne sound," explains Catherine Carr, biologist and co-author of the study. "But this ancient inner pathway, which is typically linked to balance, helps geckos detect vibrations that travel through mediums like the ground or water. This pathway exists in amphibians and fish, and now it's proven to be preserved in lizards as well. Our findings shed light on how the auditory system evolved from what you see in fish to what you see in land animals including humans."
Carr and first author, biologist Dawei Han, closely investigated the brains of tokay geckos, and found that the saccule has a direct connection to a cluster of neurons, called the vestibularis ovalis (VeO), in the hindbrain. These VeO neurons don't receive input from any other inner ear structures. Information is then passed onto the auditory midbrain, where the animal would perceive the vibrations simultaneously with sound. To confirm the saccule's role in hearing, the researchers used tungsten electrodes to monitor how VeO units responded to vibrations through a platform. They slowly cranked up the vibes from 10 to 1,000 Hertz, and found that the neurons were most sensitive to frequencies between 50 and 200 Hertz, peaking around 100 Hertz.
Finally, they checked whether the VeO units were just 'hearing' the deep, rumbling sounds produced by the vibration device via typical auditory channels. The team delivered sound stimuli to the animals' ears, at the same frequencies but louder volume — and sure enough, they didn't detect any response from the VeO units. This makes the tokay gecko the first amniote (the clade comprising all reptiles, birds, and mammals) known to use the saccule for this purpose. That said, they haven't found an obvious behavioral reason for these lizards to have dedicated vibration receptors in their heads yet. Han and Carr hypothesize tokay geckos they might use it to detect low rumbles from incoming wind, rain, and predators. And it might not be alone — a cursory survey revealed structures that look like VeO in a few other lizard and snake species, suggesting the superpower might be relatively widespread in reptiles.
Largest and Smallest Geckos
According to the Guinness Book of World records: The largest extant species of gecko is the New Caledonian giant gecko (Rhacodactylus leachianus), aka Leach’s giant gecko, which can reach lengths of 30 centimetres (11.8 inches) from snout to vent, or around 36 centimetres (14 inches) when including its stumpy tail. Adult specimens weigh in the region of 200–300 grams (7–10.5 ounces). Endemic to the South Pacific island of New Caledonia and nearby isles, this reptile is a tree-dwelling species that is mainly active at night, when it feeds on insects, fruit, spiders and sap, among other things.
According to local folklore, New Caledonian giant geckos are able to steal a person’s soul. That superstition, along with their growl-like vocalizations, have led to them gaining the nickname of “devils in the trees”. There have been reports that this species may be capable of parthenogenesis – the ability for females to produce offspring without a male – but this has yet to have been scientifically confirmed.
The largest gecko ever is the extinct Delcourt’s giant gecko (Hoplodactylus delcourti) of New Zealand, known from only a single mounted taxidermy specimen, measuring a total length (including the tail) of 61 cm (2 ft). It had been on display at the Marseilles Natural History Museum in France for more than a century before it was recognized by the curator, Alain Delcourt, in 1979.
At the other end of the spectrum, the smallest living geckos are the dwarf geckos of the genus Sphaerodactylus. Two in particular – S. ariasae from the Dominican Republic and S. parthenopion of the British Virgin Islands – stand out for their diminutive dimensions, with adult examples of both recorded at 16–18 mm (0.62–0.7 in) from snout to vent. This puts them among the world’s smallest reptiles, only surpassed by Madagascar’s leaf chameleons which can reach as small as 14 mm (0.55 in).
Gecko Mating, Reproduction and Offspring
Geckos tend to be polygynandrous (promiscuous), with both males and females having multiple partners. They engage in seasonal breeding and year-round breeding. Some engage in sperm-storing (producing young from sperm that has been stored, allowing it be used for fertilization at some time after mating). Before young are born their sex is determined by nest temperatures during a critical period, usually towards the middle of the incubation period. There is no post-hatching care. [Source: Krista Wu, Animal Diversity Web (ADW) /=]
Common house geckos are oviparous, meaning that young are hatched from eggs. According to Animal Diversity Web: But unlike most reptilian species, their eggs are round and hard-shelled, which makes them more resistant to moisture and increases their chances of survival when moved around. Eggs must incubate at a minimum of 28 degrees Celcius in order for development to occur. Three to four weeks after fertilization, females lay two eggs that partially adhere to a surface. Young ones grow fast and can become sexually mature in about six months to a year.
Mating of common house geckos involves a short courship where the male repeatedly touches the female with his snout and may bite or hold her by the neck. In tropical areas, breeding occurs throughout the year. In cooler climates, breeding is more seasonal. This vocal species give out its distinctive three to five-note call as it approaches a female for courtship, and again after mating.
Some geckos reproduce asexually. Males of those who don’t usually ignore females. When they are in the mood they wag their tails briefly and copulate Females lay their eggs in one or two clutches often in crevices or walls. The eggs hatch after about 50 days.
Image Sources: Wikimedia Commons
Text Sources: Mostly National Geographic articles. Also Life on Earth by David Attenborough (Princeton University Press), New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.
Last updated February 2025