( cxxii ) 



believers in natural selection may properly be asked to bring 

 evidence of the existence of a struggle in which the high 

 elaboration of the instincts in question is a defence. There is 

 no difficulty in meeting the challenge, for specially directed 

 observation at once reveals the existence of a keen struggle in 

 which the concealment of the cocoon is the criterion of life or 

 death. 



My attention was first directed to this particular aspect of 

 the struggle for existence in insects, on April 12, 1893, when 

 I found on the bark of Populus nigra, near Yoxford, Suffolk, 

 a cocoon of Dicranura bifida which had been opened by some 

 enemy, and the pupa removed. The observation is, I believe, 

 a common one, in fact Commander Walker and Mr. Holland 

 inform me that it is usually difficult to find cocoons of this 

 species which have not been thus attacked. Nevertheless, for 

 the sake of those who have not had the experience, I think it 

 is worth while to re-describe the evidence which certainly 

 justifies us in inferring that " an enemy hath done this." 



" The edges of the opening were still brown and fresh, as 

 was the interior of the cocoon ; and the larval skin remained f i*esh 

 and untouched inside. The opening was in the middle of the 

 exposed surface and not at one end, as it is when the moth 

 emerges. Besides, the cocoon had been opened and cracked by 

 a blow from some hard object, such as a bird's beak, and the 

 sharp irregular margins were quite different from those of the 

 natural opening made by the moth, doubtless by means of a 

 corrosive fluid, as in the allied species, Dicranura vinula, which 

 Mr. O. H. Latter has recently shown to secrete caustic potash 

 for this purpose. Furthermore, the moth emerges far later in 

 the year, and, had it emerged at an exceptional time, the empty 

 pupal skin would have been left behind in the cocoon. We 

 may therefore safely assume that the opening was the work of 

 an enemy, and, as the cocoon was five feet from the ground, it 

 was probably due to some tree-creeping, bark-exploring species 

 of bird. ... It is probable that the attention of the enemy 

 is directed to any cocoon-like object by the sense of sight, and 

 that the object is then tapped, and, if found to be hollow, 

 opened and the pupa devoured." * 



* " The enemies of Lepidopterous pup?e enclosed in bark-formed 

 cocoons." — " Science," xxiii, 1894, p. 62. The date of the observation is 



