INDIRECT BENEFITS DERIVED FROM INSECTS. 227 



In vain does the destructive Cecidomyia of the wheat conceal 

 its larvae within the glumes that so closely cover the grain ; 

 three species of these minute benefactors of our race, sent in 

 mercy by Heaven, know how to introduce their eggs into 

 them, thus preventing the mischief they would otherwise 

 occasion, and saving mankind from the horrors of famine.^ 

 In vain, also, the Cynips by its magic touch produces the 

 curious excrescences on various trees and plants, called galls, 

 for the nutriment and defence of its progeny: the parasite 

 species attached to it discovers its secret chamber, pierces its 

 wall, however thick, and commits the destroying egg 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, which belongs to Latreille's 

 genus Proctotrupes. Others are not more secured by the re- 

 pulsive nature of the substance they inhabit ; for two species 

 at least of Ichneumon'^ know how to oviposit it in stercorarious 

 larvas without soiling their wings or bodies. 



The ichneumonidan parasites are either external or internal. 

 Thus the species above alluded to, which attacks spiders, does 

 not live within their bodies, but remains on the outside ^ ; and 

 the larva of Opliion luteum, which adheres by one end to the 

 shell of the bulbiferous egg that produced it, does not enter 

 the caterpillar of Euprepia villica, the moth upon which it 

 feeds. ^ But the great majority of these animals oviposit 

 within the body of the insect to which 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 larvse may be formed from the fact, that out of thirty 

 individuals of the common cabbage caterpillar (the larvae of 

 Pontia Brassicce) which Reaumur put into a glass to feed, 

 twenty-five were fatally pierced by an Ichneumon {Micro- 



^ See above, pp. 135, 136. 



2 Alysia Manducator ; and another species allied to Alomyia Debellator, which 

 I have named A. Stercorator. 



3 De Geer, ii. 863. 4 Jbid. 851—855. 



Q 2 



