INDIRECT BENEFITS DERIVED FROM INSECTS. 259 



task devolves, and incalculable are the benefits which they 

 are the means of bestowing upon us ; for to them we are 

 indebted, or rather to Providence who created them for 

 this purpose, that our crops and grain, our cattle, our 

 fruit- and forest-trees, our pulse and flowers, and even the 

 verdant covering of the earth, are not totally destroyed. 

 Of these insects, so friendly to man, some exercise their 

 destructive agency solely while in the larva state ; others 

 in the perfect state only ; others in both these states ; and 

 lastly, others again in all the three states of larva, pupa, 

 and imago. For order's sake, and to give you a more di- 

 stinct view of the subject, I shall say something on each 

 separately. 



The first, those which are insectivorous only in their 

 larva state, may be further subdivided into parasites and 

 imparasites, meaning by the former term those that feed 

 upon a Hiring insect, and only destroy it when they have 

 attained their full growth ; and by the latter, those that 

 prey upon insects already dead, or that kill them in the 

 act of devouring them. 



The imparasitic insect devourers chiefly belong to the 

 Hymenoptera order ; and though it is in the larva state 

 that their prowess is exhibited, the task of providing the 

 prey is usually left to the female, of which each species 

 for the most part selects a particular kind of insect. Thus 

 many species of Cerceris and the splendid Chrysidce feed 

 upon insects of their own order. One of the latter (Pa- 

 norpes incarnata^ Latr.) commits her eggs to the progeny 

 of Bembex rostrata : another (Chrysis bidentata) attacks 

 the young of Vespa spinipes. 



Bembex and Mellinus confine themselves to Diptera^ 

 s 2 



