64 THE EVOLUTION THEORY 



animals. We are familiar with our big grass-green grasshopper, and 

 we know how easily it is overlooked when it sits quietly on a high 

 grass-stem, surrounded by grasses and herbage ; the light grass-green 

 of its whole body protects it most effectively from discovery: for 

 myself, at least, I must confess that in a flowery meadow I have 

 stood right in front of one, and have looked close to it for a long 

 time without detecting it. In the same way countless insects of the 

 most diverse groups — bugs, dipterous flies, sawflies, butterflies — and 

 especially the larvae (caterpillars) of the last, are of the same green as 

 the plants on which they live, and this again applies to the predaceous 

 species, as well as the species preyed upon. Thus the rapacious 

 praying-mantis {Mantis religiosa) is as green as the grass in which it 

 lurks motionless for its victim — a dragonfly, a fly, or a butterfly. 



There are also green spiders, green amphibians like the edible 

 frog, and especially the tree-frog, green reptiles like lizards and the 

 tree-snakes of tropical forests. It is always animals which live 

 among green that are green in colour. 



We may wonder, for a moment, why there are so few green 

 birds, since they spend so much of their time among the green leaves. 

 But this paucity of green birds is only true of temperate climates. 

 In Germany we have only the green woodpecker, the siskin, and 

 a few other little birds, and even these are not of a bright green, but 

 are rather greyish-green. The explanation lies in the long winter, 

 when the trees are leafless. In the evergreen forests of the tropics 

 there are numerous green birds belonging to very diverse families. 



Yet another group with a common colour-adaptation deserves 

 mention — the beasts of the night. They are all more or less grey, 

 brown, yellowish, or a mixture of these colours, and it is obvious that, 

 in the duskiness of night, they must blend better with their environ- 

 ment on this account. White mice and white rats cannot exist under 

 natural conditions, since they are conspicuous in the night, and the 

 same would be true of white bats, nightjars, and owls ; but all of these 

 have a coloration suited to nocturnal habits. 



A very remarkable fact is that in many animals the colour- 

 adaptation is a double one. Thus the Arctic fox is white only in 

 winter, while in summer he is greyish-brown ; the ermine changes 

 in the same way, and the great white snowy owl of the Arctic regions 

 has in summer a grey-brown variegated plumage. Many animals 

 which are subject to persecution also change colour with the 

 seasons, like the mountain hare (Lepus variabilis), which is brown 

 in summer and pure white in winter, the Lapland lemming, and 

 the ptarmigan (Lagopus alpinus), which do the same. It has been 



