INDIRECT BENEFITS DERIVED FROM INSECTS. 253 



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 

 GasteropJiilus 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 con- 

 stant motion in which they are kept in summer by the 

 attacks of the Stomoxys and other flies, may prevent dis- 

 eases that would be brought on by indolence and reple- 

 tion. And in the case of man himself, if I do not go so 

 far as with Linne to give the louse the credit of preserv- 

 ing 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 per- 

 ceive have an intimate bearing upon it; and I shall there- 

 fore proceed to point out the more evident benefits 

 which we derive from insects, arranging them under the 

 two great heads of direct benefits, and those which are 

 indirect ; beginning with the latter. 



