INDIRECT BENEFITS DERIVED FROM INSECTS. 145 



makes it an object of cultivation, must expect that these agents will follow 

 it into the artificial state in which he has placed it, and still prey upon it ; 

 and it is his business to exert his faculties in inventing means to guard 

 against their attacks. It is a wise provision that there should exist a race 

 of beings empowered to remove all her superfluous productions from the 

 face of nature ; and in effecting this, whatever individual injury may arise, 

 insects must be deemed general benefactors. Even the locusts, which lay 

 waste whole countries, clear the way for the renovation of their vegetable 

 productions, which were in danger of being destroyed by the exuberance of 

 some individual species, and thus are fulfilling the great law of the Cre- 

 ator, that of all which he has made nothing should be lost. A region, 

 Sparrman tells us, which had been choked up by shrubs, perennial plants, 

 and hard half-withered and unpalatable grasses, after being made bare by 

 these scourges, soon appears in a far more beautiful dress, clothed with 

 new herbs, superb lilies, and fresh annual grasses, and young and juicy 

 shoots of the perennial kinds, affording delicious herbage for the wild 

 cattle and game. 1 And though the interest of individual man is often 

 sacrificed to the general good, in many cases the insect pests which he 

 most execrates will be found to be positively beneficial to him, unless when 

 suffered to increase beyond their due bounds. Thus the insects that 

 attack the roots of the grasses, and, as has been before observed, so ma- 

 terially injure our herbage, the wire-worm, the larvae of Melolontha vul- 

 garis y Tipula oleracea, &c., in ordinary seasons only devour so much as is 

 necessary to make room for fresh shoots, and the production of new 

 herbage; in this manner maintaining a constant succession of young 

 plants, and causing an annual though partial renovation of our meadows 

 and pastures. In the rich fields near Rye in Sussex I particularly observed 

 this effect ; and I have since at home remarked, that at certain times of 

 the year dead plants may be everywhere observed, pulled up by the cattle 

 as they feed, whose place is supplied by new offsets. So that, when in 

 moderate numbers, these insects do no more harm to the grass than would 

 the sharp-toothed harrows which it has been sometimes advised to apply to 

 hide-bound pastures, and the beneficial operation of which in loosening 

 the sub-soil these insect borers closely imitate. 



Nor would it be difficult to show that the ordinary good effects of some 

 of those insects, which torment ourselves and our cattle, preponderate over 

 their evil ones. Mr. Clark is inclined to think that the gentle irritation 

 of CEstrus Equi is advantageous to the stomach of the horse rather than 

 the contrary. On the same principle it is not improbable that the Tabani 

 often act as useful phlebotomists to our full-fed animals ; and that the 

 constant motion in which they are kept in summer by the attacks of the 

 Stomoxys and other flies may prevent diseases that would be brought on 

 by indolence and repletion. And in the case of man himself, if I do not go 

 so far as Linne to give the louse the credit of preserving full-fed boys from 

 coughs, epilepsy, &c., we may safely regard as no small good the stimulus 

 which these, and others of the insect assailants of the persons of the dirty 

 and the vicious, afford to personal cleanliness and purity. 



I might enlarge greatly upon the foregoing view of the subject, but this is 

 unnecessary, as numerous facts will occur in subsequent letters which you 

 will readily perceive have an intimate bearing upon it ; and I shall, there- 



1 Span-man's Voyage, i. 867. 



