150 INDIRECT BENEFITS DERIVED FROM INSECTS. 



insects to which this duty is intrusted have been already mentioned in a 

 former letter ; but none of them do their business so expeditiously or 

 effectually as the Termites, which ply themselves in such numbers and so 

 unremittingly, that Mr. Smeathman assures us they will in a few weeks 

 destroy and carry away the trunks of large trees, without leaving a particle 

 behind ; and in places where, two or three years before, there has been a 

 populous town, if the inhabitants, as is frequently the case, have chosen to 

 abandon it, there shall be a very thick wood, and not the vestige of a post 

 to be seen. 



I observed in a former letter, that the devastations of insects are not the 

 same in every season, their power of mischief being evident only at cer- 

 tain times, when Providence, by permitting an unusual increase of their 

 numbers, gives them a commission to lay waste any particular country or 

 district. The great agents in preventing this increase, and keeping the 

 noxious species within proper limits, are other insects ; and to these I 

 shall now call your attention. 



Numerous are the tribes upon which this important 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 distinct 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 living 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 Chrysida or golden wasps feed upon 

 insects of their own order. One of the latter (Parnopes mcarnatd) com- 

 mits her eggs to the progeny of Sembex rostrata : another (Chrysis biden- 

 fata) attacks the young of Epipone spinipes. 



Sembex and Mellinus confine themselves to Diptera, the former preying 

 upon Eristalis tenax y Bombylii, and the like * ; the latter, amongst others, 

 ridding us of the troublesome Stomoxys calcitrans. One of these last I have 

 observed stationed on dung watching for flies, which, when seized, she 

 carried to her burrow. The numerous species of Crabro Fab. also store 

 up chiefly dipterous insects in their cells, some confining themselves to one 

 and the same species, others apparently taking any that offer. 



Epipone spinipes, belonging to the family of Wasps, feeds upon certain 

 green apod larvae, of which the female deposits ten or twelve with each 



1 Latreille, Observations nouvelles sur les Hymenopteres. Annal de Mus. 11. 



