The colour of animals is by no means a matter of chance; it depends on many considerations, but in the majority of cases the choice tends to protect the animal from danger by rendering it less conspicuous. Perhaps, it may be said that if colouring is mainly protective, there ought to be but few brightly coloured animals. There are, however, not a few cases in which vivid colours are themselves protective. The kingfisher, though so brightly coloured, is by no means easy to spot. The blue harmonizes with the water, and the bird looks almost like a flash of sunlight as it darts along the stream.

Desert animals are generally the colour of the desert. Thus, neither the sparse trees nor the feeble undergrowth such as twigs and small branches provide even the slightest protection from their foes. Hence, a modification, requiring their colour blending with that of their surroundings, is absolutely necessary. Without exception, the upper plumage of every bird and also the skin of all snakes and lizards, is of one uniform sand colour.

The next point is the colour of mature caterpillars, some of which are brown. This probably makes the caterpillar even more conspicuous among the green leaves than would otherwise be the case. Let us see, then, whether the habits of the insect can protect it. What would you do if you were a big caterpillar? Why, like most other defenceless creatures, you would feed by night, and lie concealed by day. So do these caterpillars. When the morning light comes, they creep down the stem of the food plant, and lie concealed among the thick foliage, dry sticks and leaves, near the ground, and it is obvious that under such circumstances the brown colour really serves as protection.