376 



LETTEK XXVII. 

 ON THE INSTINCT OF INSECTS. 



The greater part of those surprising facts connected with 

 the manners and economy of insects, of which the relation 

 has occupied the preceding letters, is to be referred, I have 

 told you, to their instinct. But what, you will ask, is this 

 instinct? — of what nature is this faculty which produces 

 effects so extraordinary ? 



To this query I do not pretend to give any satisfactory 

 answer. As I am quite of Bonnet's opinion, that philosophers 

 will in vain torment themselves to define instinct, until they 

 have spent some time in the head of an animal without 

 actually being that animal — a species of metempsychosis 

 through which I have never passed — I shall not attempt 

 to explain what this mysterious energy is. It will not, 

 however, I imagine, be very difficult to show what it is 

 not ; and some observations with this view, followed by an 

 enumeration of peculiarities which distinguish the instincts 

 of insects from those of other tribes of animals, and a short 

 inquiry whether their actions are guided solely by instinct, 

 will form the substance of this letter. 



I. It is quite superfluous at this day to controvert the 

 explanations of instinct advanced by some of the philosophers 

 of the old school, such as that of Cudworth, who referred 

 this faculty to a certain plastic nature ; or that of Des Cartes, 

 who contended that animals are mere machines. Nor, I 

 fancy, would you thank me for entering into an elaborate 

 refutation of the doctrine of Mylius, that many of the actions 

 deemed instinctive are the effect of painful corporeal feelings ; 

 the cocoon of a caterpillar, for instance, being the result of a 

 fit of the colic, produced by a superabundance of the gum 

 which fills its silk-bags, and which exuding is twisted round 

 it by its uneasy contortions into a regular ball. Still less 



