BUTTERFLIES AND MIMICRY 



sleeping in a world infested by enemies. I presume, 

 of course, this green hairstreak sleeps on a fresh 

 green leaf. 



One fact in the sleep as distinguished from 

 the temporary day repose of these four or five 

 species seemed to me at first to tell in favour of 

 the theory that the butterfly puts out of sight its 

 striking colours and marks, unless these match its 

 environment ; namely, the habit these butterflies, 

 also the large heath, grayling, and others, have 

 of lowering the folded upper wings till only 

 the tips can be seen. Thus in sleep they show 

 scarcely more than the under side of the under 

 wings. The spots and " eyes " on the under sides 

 of the upper wings of the meadow-brown, small 

 copper, small heath, and large heath are thus put 

 out of sight, with the result that the sleeper is 

 less noticeable. A few seconds after the butterfly 

 has perched for sleep it draws down its upper wings, 

 and the "eye" disappears. But I now think that 

 the object of this is not harmony with environment. 

 It is likelier the butterfly does this to economize 

 the extent of wing surface exposed to weather. 

 A butterfly should not waste its ornaments on the 

 night ; as it is, they are spoilt too soon ; you can 

 almost see through the edges of the battered wings 

 of dark green fritillaries and large heaths that linger 

 in the woods to-day. 



209 



