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Find, identify & discuss the marine species of SANParks
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Honorary Virtual Ranger
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Unread post by DuQues » Wed Apr 19, 2006 1:25 pm

Class Reptilia (reptiles)
Order Squamata (lizards and snakes)
Suborder Lacertilia (lizards)
Family Gekkonidae (geckos)

About 400 species exist.


Geckos live in a variety of warm habitats, including rainforests, deserts, grasslands, and marshes.

Geckos have short, wide, fleshy toes with large, backward-curved claws. Most geckos have sticky toe pads, sesert geckos have fringed feet that let them run across sand very easily. Flying geckos (genus Ptychozoon) have wide flaps of skin extending from the abdomen and have webbed toes, legs, and tail that help them glide gracefully through the air.
Geckos range in size from 1.5 to 35 cm long, the largest gecko is the Tokay gecko (Gecko gecko).
Geckos are the only lizards that have a voice. Some species of geckos make a squeaking or clicking noise that sounds like "gecko," hence their name.

Most geckos are tan to dark grey, subtly patterned, and somewhat rubbery looking. Some species can change color to blend in with their surroundings or with temperature differences. However others can be brightly colored. Geckos regularly shed their skin.

Many species have specialized toe pads that enable them to climb smooth vertical surfaces and even cross indoor ceilings with ease. (More on that below.) 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 seldom really discouraged because they feed on insect pests. Many geckos are kept as pets, the most popular is the Leopard Gecko (Eublepharis macularius). They are arboreal and nocturnal so you will not see them much during the daytime hours.

With eyesight comparable to a cat's, geckos can see better than any other lizard. Geckos cannot blink since instead of an eyelid they have one transparent scale, which covers the eye. If their eyes are dirty, the gecko licks them clean with its large fleshy tongue.

Gecko are carnivores. They eat mostly insects (like crickets, springtails, and cockroaches) and mealworms, but they also eat young birds, eggs, and tiny mammals, hunting for their prey at night.

Snakes are the gecko's main predators. As a defense against predators Gecko's will drop their tails. A muscular spasm separates the tail at a specialized fracture point found in some of the tail vertebrae while a related adaptation clamps off blood vessels to prevent hemorrhaging. A new tail will begin to grow in a few weeks, but instead of a column of distinct bony vertebrae, it will have a less flexible rod of calcified cartilage. If the remaining original part still has a fracture point, the lizard can autotomize its tail again. A newly lost tail twitches violently until the nerve impulses run down, and is very likely to hold the predator's attention while the lizard escapes. Arboreal species, which use their tails extensively as a fifth limb when climbing, are less likely to drop the tail than ground dwelling species.
Geckos use the tail for fat storage, so the gecko needs to have plenty food until the tail has regrown.

Geckos are quite prolific breeders. Mating usually occurs at night and two eggs will generally be laid after around 60-70 days. Incubation time ranges from 39 to 62 days. The females can lay up to five clutches a year. The temperature at which the eggs incubate decides the sex of the young ones. The rule of thumb for Leopard Gecko is that eggs incubated at 26°C result in female hatchlings. Male hatchlings will be produced at 32°C, and at 29°C a percentage of both sexes will be realized. The eggs are soft at first, but harden quickly. There is no parental care. Geckos will sometimes eat their own eggs.

Some species are parthenogenic, the females capable of reproducing without copulating with a male. This improves the geckos' ability to spread to new islands.

This depends on the species of course, but they can reach ages of around 20 years, and in captivity even 36 years has been reported.

How do they stick?
The little lizards have a network of tiny hairs and pads on their feet which produce electrical attractions that literally glue the animals down. With millions of the hairs on each foot, the combined attraction of the weak electrical forces, known as Van der Waal forces, that allow the gecko to stick to virtually any surface - even polished glass. Geckos have developed an amazing way of walking that rolls these hairs onto the surface, and then peels them off again, just like tape.
There are millions of micron-scale adhesive foot-hairs on each toe. Each foot-hair splits into hundreds of tips only 200 nanometers in diameter, permitting intimate contact with rough and smooth surfaces alike. Geckos' adhesive microstructure requires minimal attachment force, leaves no residue, is directional, detaches without measurable forces, is self-cleaning, and works underwater, in a vacuum, and on nearly every surface material and profile.
A single gecko foot hair (which is named a seta) was taken and direct measurement of its adhesive function was taken.

It was discovered that the seta is 10 times more adhesive than predicted from prior measurement on whole animals. The adhesive is so strong that a single seta can lift 20 mg (The weight of an ant.). A million setae could lift the weight of a child (20kg). A million setae could easily fit onto the area of a Dime. The combined attraction of a billion spatulae is a thousand times more than a gecko needs to hang from the ceiling. Maximum potential force of 2,000,000 setae on 4 feet of a gecko = 2,000,000 x 200 micronewton = 400 newton = 40788 grams force, or 40 kilo's! This is 600 times greater sticking power than friction alone can account for.

Van der Waals forces
Named after a 19th-century Dutch physicist, van der Waal forces are weak electrodynamic forces that act over relatively short distances and are responsible for the cohesion of molecular crystals and liquids. The forces stem partly from dipole to dipole interactions, but even nonpolar molecules and atoms exert a certain attraction to one another. Ultimately, this short-range molecular attraction allows the gecko to stick to nearly every surface.


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