150 INDIRECT BENEFITS DERIVED FROM INSECTS. 
insects to which this duty is intrusted haye 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. 
T observed in a former letter, that the devastations of insects are not the 
same in eyery 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 L 
shall now call your attention. 
Numerous are the tribes upon which this important task devolves, and 
incalculable are the benefits which they ave 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 /arva state, may be 
| further subdivided into parasites and imparasites, meaning by the former 
‘term those that feed upon a diving insect, and only destroy it when they 
{ have attained their full growth; and by the latter, those that prey upon 
f 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 purt selects a particular kind of insect. Thus many 
species of Cerceris and the splendid Chryside or golden wasps feed upon 
insects of their own order. One of the latter (Parnopes incarnata) com- 
mits her eggs to the progeny of Bembew rostrata: another (Chrysis biden- 
fata) attacks the young of Wpipone spinipes. ‘ 
Bembex and Mellinus confine themselves to Diptera, the former preying 
upon Eristalis tenax, Bombylii, and the like1; the latter, amongst others, 
ridding us of the troublesome Stomowxys 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 Hyménoptéres. Annal. de Mus. 11, 
