NOW YOU SEE ME...

Some animals use colour change to blend into the background; for others it is a powerful form of communication. But how exactly do they do it?

- Laurie Jackson

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. The arachnids take about a week to morph from white to yellow, hiding in plain sight against their preferred backdrop of golden blooms.

For crustaceans, a slow colour change allows them to adapt to alterations in their environment. Chameleon prawns, for instance, transition between green and red, tracking the seasonal appearance of seaweed in their rocky shore habitat; shore crabs take on a more uniform colour as they mature, allowing them to blend in as they migrate onto the seabed of the subtidal zone.