156* NATURAL ARRANGEMENT OF INSECTS. 



cidental to their mode of parasitism, deposit their eggs 

 either upon or within the egg or larva of the insect 

 upon which they are parasitical. The young, when dis- 

 closed,, if deposited upon the surface, eats its way into 

 the insect upon which it preys ; but yet, guided by its 

 instinct, it feeds so cautiously as not to interrupt the 

 vital functions, and the creature progresses to the ma- 

 turity of the pupa state, but, of course, in a sickly con- 

 dition. Having undergone this change, its insidious 

 enemy still lurking within it, its existence then draws to 

 a close, for the parasite, becoming less restricted in 

 its diet, consumes all before it; and having by that time 

 acquired its full growth, it transforms either within the 

 husk of the insect upon which it had preyed, or it 

 pierces through this and spins its cocoon, and therein 

 takes its metamorphosis upon the surface of this case. 

 Sometimes a larva feeds but one of these parasites, 

 when it consists of the larger normal Ichneumones; but 

 myriads at other times inhabit it, when these are com- 

 posed of Chalcidites. In these last instances, more than 

 one species frequently prey at the same time upon the 

 devoted victim, as we have repeatedly had occasion to 

 observe, and much to our vexation; for, after having used 

 every precaution to rear some rare lepidopterous larva, 

 we have found all our assidous exertions thwarted by 

 these tiny foes. It is not, however, the Lepidoptera 

 alone that are subjected to these attacks, but some prey 

 likewise on the Coleoptera ; and it is not improbable that 

 all the orders may be infested by them, they having so 

 little fellow feeling as to be destructive even to their 

 own order. The second kind of parasites are those 

 which occur in our group of Sphecides : these deposit 

 their eggs within the nests of other Spheces, frequently 

 of the same genus as themselves, for the purpose of being 

 nurtured at the expense of the young, by consuming the 

 food laid up in store by the provident parent; and, 

 doubtlessly, these insects, being predatorial and carni- 

 vorous, feed upon the unhappy larva itself. An awk- 

 ward collision must of course sometimes occur, where 



