The spectacularly colourful world of panther chameleons (pictures)

The colour change mechanism in chameleons has only recentlybeen revealed. It had previously been supposed that, like squids and octopuses, it was caused by organelles within pigment-changingcells called chromatophores.

Instead, as discovered by a team of researchersat the University of Geneva, the chameleon's ability to change the colour ofits skin is thanks to a lattice of nanocrystals inside a thick layer of dermal iridophores,or iridescent chromatophores. See it in action here.

Chameleon feet, from a distance, look like they each onlyhave two toes, which they use to grip branches. Get a little closer and you'llsee something strange: one "toe" has three claws and the other hastwo. This is because each toe is actually a fused bundle of toes. On itsforelimbs, the outer bundle contains two toes, and the inner bundle three; onthe hindlimbs, the outer bundle has three toes and the inner bundle has two.Adorbs!

Chameleon eyes are unique among reptiles: the eyelids arefused, leaving only a hole just large enough for the pupils to peer through. Theentire structure can pivot, giving the chameleon 360-degree vision around theirbodies. Even more neat: each eye can move and see independently from the other,meaning that chameleons can look in two separate places at the same time. They usemonocular depth cues, which provide depth information to a single eye, to locate prey.

Chameleons don't just use their gorgeous colours to hideamong their environments. They use it for social purposes as well. Males, whichare typically more elaborately coloured than females for this very reason, usetheir colours for courtship displays for the ladies, or for displays ofaggression against other males or threats. Lighter colours are usually forwooing purposes, while darker colours are more intimidating. Males alsotypically have more ornamentation, such as horns and spikes.

Chameleons are exclusively "old world"lizards, found in Africa, Europe and Asia -- the parts of the world known toEuropeans before contact with the Americas. Around half of the world'schameleon species are native to Madagascar, according to Wild Madagascar. The American chameleon, as it is called, is not a chameleon atall -- it's a different kind of lizard, the Carolina anole. It canstill change colour, though.

Chameleons have very long tongues that they use to snaginsects -- around 1.5 to two times the length of their bodies, although thisproportion is greater in smaller chameleons. Powerful muscles in thechameleon's throat whip the tongue outwards at extremely high speeds -- 26 bodylengths per second, or 21.6 kilometres (13.4 miles) per hour. The accelerationrate is phenomenal, from 0 to six metres (20 feet) per second in 20 milliseconds, a rate fasterthan muscles could achieve alone. A collagen structure in the mouth of thechameleon acts as a catapult; this is how it achieves such incredible acceleration.

Compared to other reptiles, chameleons have magnificentvision: they can see 5 to 10 metres away, all the better to see small preywith, my dear. Chameleons can also seein the ultraviolet spectrum, and they seem to thrive under ultraviolet light incaptivity; eggs irradiated with ultraviolet light are more likely to hatch and produce living young, and the animals are more social.It's hypothesised that the UV irradiation helps compensate for a lack ofvitamin D in captive environments.

There is a lot of size variation between chameleon species. The biggestis Madagascar's Malagasy giant chameleon, with a maximum lengthof 68.5cm (27 inches). The smallest is the teensy tiny Brookesiamicra, which has a maximum length of 2.9cm (1.1 inches). Pantherchameleons are somewhere in the middle, with a maximum length of around 50cm (20 inches).

Chameleons are not very social animals, coming together onlyto mate. Males will try to intimidate each other when they come into contactwith other males; males and females will mate, unless the female is alreadygravid (that is, carrying fertilised eggs). When she is gravid, the female'scolouring will change, darkening to signify to the male that she does not wantto mate. Producing eggs takes a pretty heavy toll on the female's body -- she'llproduce usually between five and eight clutches in her lifespan, which is twoto three years. That's shorter than the male's five years because of those reproductive stresses.

Chameleons are not very good listeners. Maybe they want tobe, but the fact is that they're physically incapable of it: all that ocularability has a tradeoff, and that it's that the chameleon is hard of hearing. Chameleonsdon't have middle or outer ears, just small holes in their heads that can pickup sounds in the 200 to 600Hz range. (Humans are generally accepted to have a hearing range between 20 and 20,000Hz.) Instead, chameleons rely on sensingvibrations and their eyes to navigate the world around them.