INSTINCT VERSUS EXPERIENCE 157 



easy to speak of improvement by experience, perhaps 

 easy to think of the progress of an insect's education 

 under the sternest of teachers : easy so long as we confine 

 ourselves to generalities. Attempt to picture the process 

 in a definite case, and apply it, as I have done, to account 

 for the growth of some special protective adaptation, 

 and it is instantly borne in upon us that we are placing 

 on insect psychology a load it is altogether unable to 

 bear. 



The Cocoon-making Instinct. 



There are, however, numberless examples in which it 

 is impossible that improvement could be thus effected, 

 even if insects did possess the requisite brains, that is 

 unless we also accord to them the gift of prophecy. 

 These are the cases in which instinct prepares for the 

 dangers of a struggle at some future time, when the 

 organism which manifested the instinct will have changed 

 its form, and become incapable of making further changes 

 in the means of protection, and indeed as a rule entirely 

 incapable of making any defence. 



Consider, for example, another observation made by 

 Mr. Hamm in July, 1900, upon the cocoons of Malaco- 

 soma neustria (the common ' Lackey Moth ') spun within 

 the leaves of black-currant and apple in his garden at 

 Oxford. These he found to be opened by birds, probably 

 sparrows, which had pecked a hole in the leaf, thus 

 breaking through the cocoon at its thinnest point, 1 and 

 abstracted the chrysalis. 



1 The cocoons were exhibited to the Entomological Society on 

 March 19, 1902. See Proc. Ent. Soc. Land., 1902, p. xv. 



Mr. W. Holland many years ago showed that birds attack in this 

 particular way, but his observation was upon larvae spun between leaves, 

 and not pupae ; and the latter are specially suited for enforcing the present 

 argument. Mr. Holland's observation is as follows : 



'On the 6th of this month [June, 1890, near Reading] Capt. 

 Robertson and I went to get some larvae of popuhli from some low 

 trees of Populus iremula which were covered with that species. Capt. 

 Robertson had picked off about 100 larvae the night before; but this 

 morning when we arrived at the trees, we found some starlings had also 

 discovered the caterpillars, and had gone over the trees systematically 

 from branch to branch, pecking a hole in one side of the spun together 

 leaves, and drawing out the caterpillar, and so nearly had they cleared 



