251 



LETTER XII. 



ON THE FOOD OF INSECTS. 



Insects, like other animals, draw their 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 tiny 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 

 nauseous 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 insec^n which do. But this is not all. 

 The larger herbivorous animals are confined to a foliaceous 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 (^Scolytus, &;c.) ; 

 others the exuding resinous or other excretions (^Orthotcenia Resinelld) ; 

 a third class the pith (^^geria tipuliformis) ; and a fourth penetrate into 

 the heart of the solid wood {Prionus, Lamia, Cerambyx, &.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 parenchyma, never 

 touching the cuticle (subcutaneous Tinea) ; others only the lower surface 

 of the leaf (many Tortrices) ; while a fourth description devour the whole 

 substance of the leaf (most Lepidoptera) . And of the flower- feeders, 

 while some eat the very petals (^Cucullia Verbasci, Xylina Linaria, &tc.), 



