136 A BOOK OF INSECTS 



Doubtless a closer study of insects in relation to their 

 surroundings will bring to light many similar examples of 

 obliterative shading. There is, too, the possibility of 

 optical illusion, consequent upon the relative intensity 

 and arrangement of the markings on an insect's body or 

 wings. Many dark-coloured moths, for example, have a 

 very distinct white or pale spot in the middle of each 

 fore-wing. At first thought this would seem to detract 

 from the creature's disguise ; but the reverse probably 

 holds good. The eye is at once caught and held, as it 

 were, by the conspicuous spots, and for this very reason 

 fails to detect the less obvious outline of the insect. 



Certain butterflies, when at rest with closed wings, 

 have the appearance of flowers. A remarkable example 

 is the familiar orange-tip (Euckloe cardamijies). The 

 upper surface of the wings is white, with black markings; 

 while in the male only there is a large orange area at the 

 tip of each fore- wing. When flying these insects are 

 very conspicuous, but as soon as they settle among 

 herbage they seem to drop out of existence ; the reason 

 being that the underside of the hind-wings, between 

 which the fore-wings are folded in repose, are mottled 

 with green and white in a manner which suggests an in- 

 florescence, such as that of the plant called marsh valerian. 

 That the orange-tip butterflies frequently settle upon 

 or near blooms of this kind the writer can vouch from his 

 own observations ; and when the insect composes itself for 

 a long rest, it tucks its body between its folded wings, 

 and raises the latter in a characteristic manner— a habit 

 which greatly enhances the protective resemblance. 

 Several of our common blue butterflies look like the 

 plantain heads and flowering grasses among which they 

 roost ; and when settling for the night, or in dull, windy 

 weather, they invariably turn head downwards. Indeed, 



