214 INDIRECT BENEFITS DERIVED FROM INSECTS. 



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 ob- 

 served, so materially injure our herbage, the wire-worm, the 

 larvae of Melolontha vulgaris, 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 every where observed, pulled up by the cattle as they feed, 

 whose place is supplied by new offsets. So that, when in mode- 

 rate 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 



