THE PROBLEM OF DEFENCE 165 



diverting attention from vital parts of the body. If a 

 bird, when chasing a butterfly, should strike at and pierce 

 one of these eye-spots, or grab at a tail, the damage done 

 would be slight, while the fugitive would gain time to 

 evade its pursuer. As a matter of fact, naturalists in 

 tropical countries have noticed that many of their captures 

 have their wings torn and punctured in this manner. 

 Moreover, in many of the blue butterflies and hairstreaks 

 the antenna>like tails of the hind-wings are associated 

 with small eye-spots so as to suggest the appearance of a 

 head at the wrong end of the body when the insect is at 

 rest with closed wings ; and this resemblance is enhanced 

 by a constant, slight movement of the hind-wings which 

 causes the apparent antenna? to pass and repass each other 

 in a very life-like manner. That these butterflies often 

 save their real heads at the expense of their false ones 

 seems certain, for the latter are often found to have been 

 injured, or entirely bitten away — presumably by birds, 

 lizards, and other insectivorous creatures. 



Many insects illustrate the truth of the adage that 

 discretion is the better part of valour. Thus, some 

 arboreal caterpillars, when alarmed, quickly lower them- 

 selves by a silken thread from their leafy home, and hang 

 in mid-air until the threatened danger is past, when they 

 slowly draw themselves up by gathering in the thread 

 with their jaws. Other insects of many kinds "feign 

 death " in the sense that their instincts impel them to 

 drop to the ground, and remain motionless, when stimu- 

 lated by an unwonted change in their environment, such 

 as a passing shadow. The effectiveness of this habit is 

 often enhanced by the insect's protective resemblance to 

 some inanimate object, as in the case of the raspberry 

 weevil (Otiorhyncltus picipes), which looks exactly like 

 a small nodule of the soil upon which it lies. The skip- 



