How Does Camouflage Work in Animals?

The simplest form is background matching, where colour and texture resemble the surroundings. A stick insect on a twig or a flatfish on sand is doing this.

But an animal that matches perfectly can still be given away by its outline and its shadow. That is why several other strategies exist, and most well-camouflaged animals combine more than one at the same time.

Bold patterns can be camouflage rather than display. High contrast stripes and blotches break up the recognisable edge of a body, so a predator's eye struggles to assemble it into a shape.

This is why a leopard's spots work in dappled shade and why zebra stripes are so striking. Military camouflage borrowed the idea directly, and ships in both world wars were painted in bold geometric patterns intended to confuse estimates of course and speed rather than to hide them.

Look at almost any fish, deer or bird and you will notice the back is darker than the belly. This is countershading, and it cancels the shading produced by light coming from above.

Without it, an animal lit from above looks obviously three dimensional and solid. With it, the darker top and lighter underside even out and the body reads as flat. The effect is subtle and extremely widespread, which is a good sign of how well it works.

Some animals do not hide so much as impersonate. This is masquerade, and the disguise is usually something a predator would not bother eating:

• •Leaf insects resembling leaves down to the veins and damage
• •Caterpillars shaped and coloured like bird droppings
• •Decorator crabs attaching seaweed and sponges to their shells
• •Fish shaped like drifting dead leaves

Cephalopods are the extreme case. Octopus, squid and cuttlefish have skin containing chromatophores, pigment sacs controlled by muscles, layered over reflective cells. They can change colour and pattern in under a second and also alter skin texture to mimic rough surfaces.

The strange part is that cephalopods appear to be colourblind by conventional measures, so how they match colour so well is still debated, with one hypothesis being that their oddly shaped pupils allow colour to be judged through focus. Chameleons change colour by a different mechanism involving nanocrystals in the skin, and mostly for signalling rather than hiding.

The opposite of camouflage is aposematism, where an animal advertises itself with bright warning colours because it is genuinely dangerous or foul tasting. Poison dart frogs and wasps both do this.

This creates an opening for mimicry. Harmless hoverflies have evolved wasp-like stripes, gaining protection without the cost of producing venom. Where several genuinely dangerous species converge on the same warning pattern, as many stinging insects have, predators only need to learn one lesson, which benefits all of them.

Camouflage works through background matching, disruptive patterns, countershading and outright masquerade, usually in combination, and the best camouflaged animals are solving the problems of outline and shadow as much as colour.