SOME animals do not use colours to deceive predators, but to warn them against attacking because they are either distasteful or dangerous.

Conspicuous, easily recognised colour patterns have evolved in many cases to advertise an unpleasant nature. This is an obvious advantage in saving the animal concerned from unnecessary attack. Birds soon learn to avoid the familiar yellow and black stripes of the wasp with its unpleasant sting, and the same goes for the black and orange caterpillars of the cinnabar moth, which are very distasteful.

In summer, these caterpillars can be seen in thousands feeding on the common ragwort, a plant of the daisy family, a sure indication that they must be distasteful, for otherwise they would surely be eaten up by birds that tend to concentrate on a particular food while it is available. Because of this tendency, most larvae that live in large groups need to be protected from attack; many of them are hairy and cause irritation when touched. The small tortoiseshell caterpillars, which gather in large groups, are black and yellow, and the caterpillar of the peacock butterfly, which behaves in an equally conspicuous way, is black. Yellow and black are both warning colours and very few birds will eat these caterpillars.

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Although the best-known cases of warning colouration are found among the insects, there are many larger examples too, which include American skunks that have bold white stripes on a black background, advertising highly obnoxious-smelling and pervading fluid, which they squirt at their enemies. And there is a toad, which has glands in its skin that secrete an unpleasant substance, while its underside is bright scarlet. When a potential predator, a stork for instance, flies over a group of these amphibians, they instantly flop on their backs exposing their scarlet bodies. The birds associate bright red colour with the unpleasant taste and do not try to eat the toads.

The cuttlefish, a group of cephalopod mollusks related to the squids, has an elaborate colour-change mechanism for deceiving enemies. The creature with streamlined bodies, up to 1.5 metre long and eight arms and two long tentacles at the head-end, all bearing suckers used to seize prey, when needs to make a rapid escape, it ejects the contents of its ink sac-many tiny granules of the dark-brown pigments found in the skin, melanin. Immediately after sending out this 'smoke-screen', it becomes very pale and swims away at right angles to its previous direction. The predator pursuing it is momentarily confused and attacks the cloud of pigments while the cuttlefish makes its escape.

In other cases potential predators are frightened away by some special behaviour combined with the colouring of the animal they plan to attack. Some moths, butterflies and other insects have marking on their wings that closely resembles the eye of a large and much more fearsome animal. The 'eyes' are usually concealed when the animals are at rest but are displayed when they are disturbed, and have been observed to frighten away predatory birds.

Another way of confusing the pursuer is by a sudden change from bright colours to inconspicuousness that is practised by insects such as the large yellow underwing moth with brownish or grayish upper wings and bright yellow underwings. The moth remains well-concealed when at rest, but when it flies away its colours are highly conspicuous and give a flashing sensation. At the end of the flight the insect usually descends suddenly to the ground and immediately on landing, it covers the bright parts of the body and remains very still, thus confusing the pursuer. This disappearing trick is known as 'flash colouration'.