268 INDIRECT BENEFITS DERIVED FROM INSECTS. 



cences on various trees and plants, called galls, for the 

 nutriment and defence of its progeny : the parasite spe- 

 cies attached to it discovers its secret chamber, pierces 

 its wall however thick, and commits the destroying eg^ 

 to its offspring. Even the clover-weevil is not secure 

 within the legumen of that plant; nor the wire-worm 

 in the earth, from their ichneumonidan foes. I have 

 received from the late Mr. Markwick that of the former, 

 and Mr. Paul has shown me the destroyer of the latter, 

 Avhich belongs to Latreille's genusProctotrupes. Others 

 are not more secured by the repulsive nature of the sub- 

 stance they inhabit: for two species at least of Ichneu- 

 mon^ know how to oviposit in stercorarious larvae with- 

 out soiling their wings or bodies. 



The ichneumonidan parasites are either external or 

 internal. Thus the species above alluded to, which at- 

 tacks spiders, does not live within their bodies, but re- 

 mains on the outside ^ ; and the larva of Icluieumon lu- 

 ieus, which adheres by one end to the shell of the bulbi- 

 ferous egg that produced it, does not enter the cater- 

 pillar of Bombf/x villica, the moth upon which it feeds '^. 

 But the great majority of these animals oviposit within 

 the body of the insect to A\hicli they are assigned, from 

 whence, after having consumed the interior and become 

 pupae, they emerge in their perfect state. An idea of 

 the services rendered to us by those Ichneumons which 

 prey upon noxious larvtP may be formed from the fact, 

 that out of thirty individuals of the common cabbage 

 caterpillar (the larvae ofPapilio Brassicof) which Reau- 



* I. Manducalor, Panz. Fn. Germ. 72. 4.; and another fpccics allied 

 (.0 /. Dtl/ellator, F., which 1 have named /. Stercoratvr. 

 '' IJe Geer, ii. fciGJ. ' Ibid. ^51-5, 



