Why and how do chameleons change color? asks Frank Yenna, a student in Hewlett, NY.
In their just-hanging-out colors of brown to green, scientists say, chameleons are already well camouflaged in their home habitats.
Chameleons seem to mainly shift colors in response to temperature, light and -- especially -- mood. Male chameleons change colors to intimidate other males, or, peacocklike, to attract females. Females also color-shift, signaling interest (or indifference).
More than 150 species of chameleons live on Earth, mainly in India, Pakistan, Spain, the Arabian Peninsula and across Africa.
More than half of the planet's chameleon species live on one island -- Madagascar, off Africa's southeast coast. Chameleons range from almost cat-sized (2 feet long) to minuscule -- Madagascar's Brookesia micra measures only one inch, fully grown.
Each species has evolved its own signature colors and patterns.
How does it work? Underneath the lizard's transparent outer layer of skin is a layer with red and yellow pigments. Under that is a layer of light-reflecting cells, some reflecting blue, others white. The bottom layer of skin cells contains brown melanin, the same pigment that colors human skin. A chameleon's nervous system and hormones send electrical or chemical signals, prompting pigment cells to expand or shrink. The result: quickly changing combinations of colors and patterns.
A 2013 study at Arizona State University found that male chameleons' colors become extra-bright when they're facing off over territory or competing for the attention of a female lizard. The more aggressive the male, the researchers found, the more intensely colored his stripes.
Chameleons wearing the brightest head hues were also most likely to be the victors in lizard disputes. Interestingly, the researchers discovered that how fast a male's head changed colors also predicted the winner. Like a man becoming red-faced and angry in an instant, such chameleons were the most intimidating to their rivals.
Chameleons "win" when their opponent retreats, researchers note. If a struggle ensues, it's brief, lasting five to 15 seconds. Usually, however, a chameleon's colorful "billboard" display can preempt an actual fight.
But color-shifting may also help chameleons facing a predator's attack. A study in Australia found that chameleons shown realistic models of two of their most feared predators -- a venomous tree snake or a bird that uses sharp thorns to snare the lizards -- ramped up their usual camouflaging colors.