264 INDIRECT BENEFITS DERIVED FROM INSECTS. 



rienced, than to clear a plant or small tree by placing 

 upon it several larvae of Coccinellae or of aphidivorous 

 flies collected from less valuable vegetables. 



Lastly, to close this list of imparasitic insectivorous , 

 larvae, I may mention those of Latreille's genus Voln- 

 cella (Syrphus, F.,) so remarkable for their radiated anus, 

 which live in the nests of humble bees, braving the fury 

 of their stings and devouring their young ; and the ant- 

 lion (Myrmeleon) and Reaumur's improperly named 

 worm-lion (Rhagio, F.), whose singular stratagems will 

 be detailed in a subsequent letter, both of which destroy 

 great numbers of insects that are so unfortunate as to 

 fall into their toils. 



The parasitic larvae, an extremely ' numerous tribe, 

 must next be considered. These, with the exception of 

 a very few individuals, belong to the order Hymeno- 

 ptera, and were included by Linne under his vast genus 

 Ichneumon, so named from the analogy between their 

 services and those of the Egyptian Ichneumons ( Viverra 

 Ichneumon, L.), the former as destroyers of insects, be- 

 ing equally important with the latter as devourers of ser- 

 pents, the eggs of crocodiles, &c. 



The habits of the whole of this tribe, which properly 

 includes a great number of distinct genera, are similar. 

 They all oviposit in living insects, chiefly while in the 

 larva state, sometimes while pupae (Ich. Puparum, L.) ; 

 and even while in the egg state (Ich. Ovulorum, L.); but 

 not, as far as is known, in perfect insects. The eggs 

 thus deposited soon hatch into grubs,*which immediately 

 attack their victim, and in the end ensure its destruction. 

 The number of eggs committed to each individual varies 

 according to its size, and that, of the grubs which are to 



