As the sun goes down in KwaZulu-Natal, South Africa, Australian biologist Devi Stuart-Fox and her husband Adnan Moussalli get into their yellow 1989 Volkswagen Golf and head into the iSimangaliso Wetland Park. Moussalli drives tentatively along the rough bush tracks. Stuart-Fox leans out the front passenger window, shining a torch into the rainforest.
Stuart-Fox spots something, and Moussalli stops the car. The couple get out and peer nervously into the darkness—the park’s 800 hippopotamuses roam these forests at night, and are extremely aggressive. But high above, hanging from a twisting vine, the torchlight reveals what they’re looking for: the pale, curled body of a sleeping dwarf chameleon.
Stuart-Fox climbs on top of the car with a six-metre extendable pole. Balanced on tiptoe, arms outstretched, she tickles the tiny lizard awake with the pole’s tip. The sleepy chameleon, its eyes still half closed, reaches out with its little clasping hands and grabs on.
In the morning, Stuart-Fox sets up her field station: camping table, laptop, spectrometer, fake snake, taxidermised bird, a stick, and half a dozen cloth bags containing dwarf chameleons.
She takes a still-pale male chameleon out of a bag and lets him climb onto the stick. Then she waves the bird at him. The chameleon is terrified; he swings down beneath the stick and within a few seconds has become the same grey-brown as the wood. Stuart-Fox measures the precise colour with the spectrometer.
Once the chameleon has recovered from his fright, she introduces another predator—the fake boomslang snake. Again, he tries to hide behind the stick, though the colour match isn’t quite as good. (Snakes have worse eyesight than birds, so perhaps chameleons make less of an effort.)
Finally, she places another male chameleon on the camping table. This time, instead of camouflaging, the males begin to show off. They puff out their throats and became orange, with scarlet stripes and lime-green speckles.
Most animals have a wardrobe problem. How to stand out—but also hide—if you only have one outfit? Some animals keep their glad rags concealed beneath feathers, frills, or extendable dewlaps (folds of skin hanging beneath the throat). In certain species, males are showy, while nest-guarding females are drab. European songbirds feature ultraviolet patches on their chests and foreheads that are hidden from predators without UV sight.
But a surprising number of reptiles, insects, cephalopods, crustaceans, amphibians, fish, birds and even mammals change their colouring to suit the needs of the moment.
The speed varies. Octopuses can switch looks instantaneously, chameleons shift in seconds, and grasshoppers take minutes to hours. As for arctic foxes, hares, stoats and ptarmigans, they change their coats or plumage from brown to white over several months to match their environment as the seasons change.
Chameleons, of course, are world-famous for their colour-swapping superpowers—but they can’t do it all. “Putting a chameleon on a Smarties box doesn’t work,” says Stuart-Fox. “They’re not every colour of the rainbow.”
Their skin is more like a paint box containing a small selection of colours that the chameleon can mix and match. The paint colours are specialised cells called chromatophores. One layer of chromatophores contains yellow, orange or red pigments, and beneath those cells is a layer of colourless crystals that scatter light, producing white or blue colours. Chameleons can combine these layers to produce green. Deeper still is a layer of chromatophores containing melanin, the same substance that gives our skin its colour. When these tiny melanin-packets cluster in the centre of the cells, the bright or pale colours in the layers above shine through. But when they disperse throughout the cells, the skin shades to dark brown or black.
Chameleons use colour not just for disguise, but for communication. And it’s not just males showing off; female chameleons send colourful messages, too. When females are gravid—the word for expecting eggs—and want to signal to males that they’re not available, they turn a blotchy, stripy, high-contrast black and cream. “They’ve definitely got their f— off colours,” says Stuart-Fox. On the other hand, when scientists painted model chameleons with come-hither colours—green with yellow spots—males attempted to mate with the fake females.
Changing colour has other benefits, too. Donning head-to-toe black can help these cold-blooded reptiles warm up on a chilly morning, while turning pale can reflect the midday sun and keep them cool. As long as they find an appropriate perch, that is. “Not surprisingly, camouflage trumps thermoregulation,” says Stuart-Fox, “because there’s no point being warm if you’re dead.”