216 



LETTEIl XII. 



ON THE rOOD OF INSECTS. 



Insects, like other animals, draw theiv food from the vegetable and animal 

 kingdoms : but a very slight survey will suffice to show that they enjoy a 

 range over far more extensive territories. 



To begin with the vegetable kingdom. — Of this vast field the larger 

 animals are confined to a comparatively small portion. Of the thousands 

 of plants which clothe the face of the earth, when we have separated the 

 grasses and a trifling number of herbs and shrubs, the rest are disgusting 

 to them, if not absolute poisons. But how infinitely more plenteous is 

 the feast to which Flora invites the insect tribes ! From the gigantic 

 banyan which covers acres with its shade, to the ivc\y fungus scarcely visible 

 to the naked eye, the vegetable creation is one vast banquet at which her 

 insect guests sit down. Perhaps not a single plant exists which does not 

 afford a delicious food to some insect, not excluding even those most nau- 

 seous and poisonous to other animals, — the acrid euphorbias, and the 

 lurid henbane and nightshade. Nor is it a presumptuous supposition, that 

 a considerable proportion of these vegetables were created expressly for 

 their entertainment and support. The common nettle is of little use either 

 to mankind or the larger animals ; but you will not doubt its importance 

 to the class of insects, when told that at least thirty distinct species feed 

 upon it ; and however important the oak may be to us, it is still more so 

 to the insect world, of which Rosel calculated that two hundred species 

 either feed upon it, or upon other insects which do. But this is not all. 

 The larger herbivorous animals are confined to a fbliaceous or farinaceous 

 diet. They can subsist on no other part of a plant than its leaves and 

 seeds, either in a recent or dried state, with the addition sometimes of the 

 tender twigs or bark. Not so the insect race, to different tribes of which 

 every part of a plant supplies appropriate food. Some attack its roots; 

 others select the trunk and branches; a third class feed upon the leaves; 

 a fourth, with yet more delicate appetite, prefer the flowers ; and a fifth 

 the fruit or seeds. Even still further selection takes place. Of those 

 which feed upon the roots, stem, and branches of vegetables, some 

 larvae eat only the bark; others both the inner bark and alburnum (6Vo- 

 lytus, &c.) ; others the exuding resinous or other excretions {OrlhotcEnia 

 resinella) ; a third class the pith (^Mgeria tipnliformis) ; and a fourth pe- 

 netrate into the heart of the solid wooil (^Prionus, Lamia, Ccrambyx', &c.). 

 Of those which prefer the leaves, some taste nothing but the sap which 

 fills their veins (^Aphides in all their states) ; others eat only the paren- 

 chyma, never touching the cuticle (subcutaneous Tinece) ; others only the 

 lower surface of the leaf (many Tortriccs) ; while a fourth descri,^tion de- 

 vour the whole substance of the leaf (most Lcimhptera). And of the flower- 



