PROTECTIVE COLOURING IN ANIMALS 305 



But there are far more numerous cases in which the 

 significance of colour as concealment, is not so immedi- 

 ately obvious. There are the curious stick insects, with 

 long bodies and delicate long legs, sometimes with bud- 

 like knobs on the body which look like bits of the branches 

 of trees, not merely on account of their colour, but on 

 account of their shape. Shape or modelling has a great 

 deal to do with the effective concealment of an animal. 

 Then, too, there is the curious fact that some insects (and 

 also some birds) when at rest on the stems of trees, are 

 practically invisible, but if they spread their wings are 

 conspicuous. The beech-leaf butterfly of Assam and 

 Africa is of a purple colour, marked with a great orange- 

 coloured bar on each fore j wing when the wings are open, 

 and it is obvious enough. But when the wings are closed 

 and the insect is at rest, the undersides only are seen, and 

 are coloured so as to represent the veining and fungus 

 marks of a dry brown leaf, so that not even a human 

 observer, let alone a bird or a lizard, can distinguish at 

 two-feet distance the butterfly from dried leaves placed 

 near it. 



A well-known little moth, with pale green mottled 

 wings, is the only case in which I have myself watched 

 the protection afforded by colour at work. It was on a 

 summer's evening, when I saw this little moth zigzagging 

 up and down with the most extraordinarily irregular 

 flight, and a bird pursuing it. Twice the bird swooped 

 and just missed his prey owing to a sudden turn and drop 

 on the part of the moth. And then to my great delight 

 the moth flopped against the stem of a tree on which was 

 growing a greenish-grey lichen. The bird swooped again 

 close to the tree, but failed to see the insect, and quitted 

 the chase. It took me an appreciable time to detect the 

 little moth resting against the lichen, and closely matching 

 it in colour. There are endless examples known of such 

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