INDIRECT BENEFITS DERIVED FROM INSECTS. 265 



spring from them ; being in most cases one only, but in 

 others amounting to some hundreds. 



From the observations hitherto made by entomolo- 

 gists, the great body of the Ichneumon tribe is principally 

 employed in keeping within their proper limits the infi- 

 nite host of lepidopterous larvae, destroying, however, 

 many insects of other orders ; and perhaps if the larvae 

 of these last fell equally under our observation with those 

 of the former, we might discover that few exist unin- 

 fested by their appropriate parasite. Such is the activity 

 and address of the Ichneumonida?, that scarcely any con- 

 cealment, except perhaps the waters, can secure their 

 prey from them ; and neither bulk, courage, nor ferocity 

 avail to terrify them from effecting their purpose. They 

 attack the ruthless spider in his toils : they discover the 

 retreat of the little bee, that for safety bores deep into 

 timber ; and though its enemy Ichneumon cannot enter 

 its cell, by means of her long ovipositor a she reaches the 

 helpless grub, which its parent vainly thought secured 

 from every foe, and deposits in it an egg, which pro- 

 duces a larva that destroys it b . In vain does the de- 

 structive 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 hi mercy by 

 Heaven, know how to introduce their eggs into them, 

 thus preventing the mischief they would otherwise occa- 

 sion, and saving mankind from the horrors of famine c . 

 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 



a Plate XVI. Fig. 1. h Marsham in Linn. Trans, iii. 26. 



c See above, p. 1(59-1 70, 



