Any member of a group of primarily tree-dwelling Old World lizards in the family Chamaeleonidae, characterized chiefly by their ability to change body colour. Other traits include toes fused into opposite bundles of two and three, teeth attached to the jaw edge, and a long, slender, extensile tongue. About half of the 150 species are found only in Madagascar; the others occur mostly in sub-Saharan Africa, only a few elsewhere. Most are 7–10 in. (17–25 cm) long, with a body flattened from side to side. The bulged eyes move independently. Each species can undergo a particular range of colour change. Insects are the main diet, but larger species also eat birds.
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Chameleons vary greatly in size and body structure, with total length from approximately 2.8 centimetres (1.1 in) in Brookesia minima, to 68.5 centimetres (27 in) in the male Furcifer oustaleti. There is a species, thought to be unique to Malawi's Mount Mulanje, which is 1 centimetre (0.6 in) across when fully grown. Many have head or facial ornamentation, such as nasal protrusions, or horn-like projections in the case of Chamaeleo jacksonii, or large crests on top of their head, like Chamaeleo calyptratus. Many species are sexually dimorphic, and males are typically much more ornamented than the female chameleons.
Chameleon species have in common their foot structure, eyes, lack of ears, and tongue.
Chameleons are didactylic: on each foot the five toes are fused into a group of two and a group of three, giving the foot a tongs-like appearance. These specialized feet allow chameleons to grip tightly to narrow branches. Each toe is equipped with a sharp claw to gain traction on surfaces such as bark when climbing. The claws make it easy to see how many toes are fused into each part of the foot: two toes on the outside of each front foot and three on the inside, and the reverse pattern on each hind foot.
Chameleons have a long tail that is able to curl up. It is used to balance on tree limbs. Sometimes it is used as a weapon. A chameleon uses its tail almost like a fifth leg.
Their eyes are the most distinctive among the reptiles. The upper and lower eyelids are joined, with only a pinhole large enough for the pupil to see through. They can rotate and focus separately to observe two different objects simultaneously. It in effect gives them a full 360-degree arc of vision around their body. When prey is located, both eyes can be focused in the same direction, giving sharp stereoscopic vision and depth perception. They have very good eye sight for reptiles, letting them see small insects from a long (5-10 cm) distance.
They lack a vomeronasal organ. Also, like snakes, they do not have an outer or a middle ear. This suggests that chameleons might be deaf, although it should be noted that snakes can sense vibration using a bone called the quadrateim. Furthermore, some or maybe all chameleons, can communicate via vibrations that travel through solid material like branches.
Chameleons have very long tongues (sometimes longer than their own body length) which they are capable of rapidly extending out of the mouth. The tongue extends out faster than human eyes can follow, at around 26 body lengths per second. The tongue hits the prey in about 30 thousandths of a second. The tongue has a sticky tip on the end, which serves to catch prey items. The tongue's tip is a bulbous ball of muscle, and as it hits its prey, it rapidly forms a small suction cup. Once the tongue sticks to a prey item, it is drawn quickly back into the mouth, where the chameleon's strong jaws crush it and it is consumed. Even a small chameleon is capable of eating a large locust or mantis. Ultraviolet light is part of the visible spectrum for chameleons. Chameleons exposed to ultraviolet light show increased social behavior and activity levels, are more inclined to bask and feed and are also more likely to reproduce as it has a positive effect on the pineal gland.
More than 160 species of Chameleons are known, arranged in nine genera. The main distribution of Chameleons is in Africa and Madagascar, and other tropical regions, although some species are also found in parts of southern Europe and Asia. There are introduced, feral populations of veiled and Jackson's chameleons in Hawaii and isolated pockets of feral Jackson's chameleons have been reported in California and Florida.
Chameleons inhabit all kinds of tropical and mountain rain forests, savannas and sometimes semi-deserts and steppes. They are mostly arboreal and are often found in trees or occasionally on smaller bushes. Some smaller species live on the ground under foliage.
The oviparous species lay eggs after a 3-6 week gestation period. The female will climb down to the ground and begin digging a hole, anywhere from 10-30 centimetres (4-12 in) deep depending on the species. The female turns herself around at the bottom of the hole and deposits her eggs. Once finished, the female buries lina and leaves the nesting site. Clutch sizes vary greatly with species. Small Brookesia species may only lay 2-4 eggs, while large Veiled Chameleons (Chamaeleo calyptratus) have been known to lay clutches of 80-100 eggs. Clutch sizes can also vary greatly among the same species. Eggs generally hatch after 4-12 months, again depending on species. The eggs of Parson's Chameleon (Calumma parsonii), a species which is rare in captivity, are believed to take upwards of 24 months to hatch.
The ovoviviparous species, such as the Jackson's Chameleon (Chamaeleo jacksonii) have a 5-6 month gestation period. The newborn are in a transparent membrane and they are still sleeping, once they touch the ground or branch, they will wake up and attempt to crawl out of the membrane. The female can have 8-30 live young at once.
Chameleons generally eat locusts, mantis, crickets, grasshopper and other insects, but larger chameleons have been known to eat small birds and other lizards. A few species, such as Jackson's Chameleon (C. jacksonii) and the Veiled Chameleon (C. calyptratus) will consume small amounts of plant matter. Chameleons prefer running water to still water.
Chameleons require lots of vitamins and minerals. To ensure sufficient nutrients, zoo-keepers "gut-load" insects before feeding them to chameleons, by rearing them on a diet of carrots, potatoes, fish flakes (tropical), dry puppy food, dark, leafy greens, etc. and dusting them with vitamin and mineral powders.
Chameleons change their colour in response to light exposure and ambient temperature, as well as to express their mood. Emotions and attraction of a mate can induce the colour change.
Different chameleon species are able to change different colours which can include pink, blue, red, orange, green, black, brown and yellow.
Chameleons are naturally coloured for their surroundings as a camouflage. However, recent research has indicated that Chameleons may use colour changes as a method of communication, including to make themselves more attractive to potential mates.
Chameleons have specialized cells, collectively called chromatophores, that lie in layers under their transparent outer skin. The cells in the upper layer, called xanthophores and erythrophores, contain yellow and red pigments respectively. Below these is another layer of cells called iridophores or guanophores, and they contain the colourless crystalline substance guanine. These reflect, among others, the blue part of incident light. If the upper layer of chromatophores appears mainly yellow, the reflected light becomes green (blue plus yellow). A layer of dark melanin containing melanophores is situated even deeper under the reflective iridophores. The melanophores influence the 'lightness' of the reflected light. All these pigment cells can rapidly relocate their pigments, thereby influencing the colour of the chameleon.
Chameleon Climbing a tree in World Buffalo Park.