NOW YOU SEE ME...
Years ago, during a field trip to the Scottish island of Cumbrae, I came face to face with a stout bobtail squid. As I watched, rapt, the tiny mollusc blushed from ghostly pale to deep red and back again, like a magic performance. But this was no illusion.
Squid are part of a whole spectrum of species that are able to change colour – an ability that comes with several speed settings. At its more relaxed end there is a handful of birds and mammals – including the Arctic fox, willow ptarmigan and snowshoe hare – that undergo a seasonal whitening triggered by waning day length. The transformation occurs as pigment disappears from fur and feathers. In mammal fur, this makes space for more air, which provides the added bonus of extra insulation as temperatures plummet.
Other environmental factors, such as ultraviolet, diet and surroundings, can also trigger gradual colour changes, involving alterations to the type and concentration of pigments within skin, exoskeleton, feathers or fur. A diet-driven transition is performed by several species of crab spiders, which ambush flower-visiting insects.
