68 THE EVOLUTION THEORY 



atropos) this sounds almost incredible, for this form is chiefly a bright 

 golden yellow, and the narrow white oblique stripes have sky-blue 

 borders becoming darker towards the under side ; but it must not be for- 

 gotten that the potato is not the true food-plant of the species, for it lives, 

 in its true home in Africa, and also in the south of Spain, on wild 

 solanaceous plants, which, we are informed by Noll, have precisely 

 these colours — golden-yellow and blue in the blossom, the fruit, and in 

 part also in the leaves and stem. There the caterpillars sit the whole 

 day long on the plants, while with us they have formed the habit of feed- 

 ing only in the twilight and at night, and concealing themselves in the 

 earth by day, a habit that is found in other caterpillars also, and 

 which we must again ascribe to a process of natural selection. 



Some caterpillars exhibit other, more complex markings, which 

 do not protect them by rendering them difficult to detect, but by 

 terrifying the enemy who has discovered them, and warning him 

 away. Such terrifying or aggressive colours are to be found, for 



Fig. 4. Full-grown caterpillar of the Elephant Hawk-moth (Chcerocampa elpenor) in its 

 " terrifying attitude." 



instance, in the caterpillars of the Sphingid genus Cheer 'ocampa in 

 the form of large eye-like spots, which occur in pairs close together 

 on the fourth and fifth segments of the animal. Children and those 

 unfamiliar with animals take these for true e} T es ; and as the 

 caterpillar, when it is threatened by an enemy, draws in the head and 

 anterior segments, so that the fourth one is greatly distended, the 

 eye-spots seem to stand on a thick head (Fig. 4), and it cannot be 

 wondered at that the smaller birds, lizards, and other enemies are 

 so terrified that they refrain from attacking. Even hens hesitate to 

 seize such a caterpillar in its defiant attitude, and I once looked on 

 for a long time in a hen-coop while one hen after another rushed to 

 pick up a caterpillar I had placed there, but, when close to it, hastily 

 drew back the head already prepared to strike. Even a gallant 

 cock was a long time in making up his mind to attack the terrible 

 beast, and drew back repeatedly before he at length ventured to strike 

 a deadly blow with his bill. After the first stroke the caterpillar, of 

 course, was lost. Thus even this disguise is only a relative protection, 

 effective only against smaller enemies. But that these are really 

 frightened away, I had once an opportunity of observing, when I put 



