44 THE BOOK OF BRITISH BUTTERFLIES. 



within bounds. Birds destroy them wholesale, while 

 none too seldom they meet the fate of their food-plant, 

 being cooked and sent to table with it. But they, as 

 well as other larvae, are subject to the attacks of ich- 

 neumon flies, each species, as a rule, having its own 

 particular parasite. These deposit their .eggs within the 

 body of their prey, and when hatched the ichneumon 

 grubs feed on the non-vital parts of the caterpillar, till 

 it is on the point of pupating, when they eat their way 

 out and spin a number of small yellow cocoons around 

 their dying host. The appearance of the ichneumon 



FIG. 21. ICHNEUMON FLY OF P. BRASSIC^E. 



of the Large White will be gathered from Fig. 21, which 

 is magnified about eight diameters.. In all four species the 

 pupae, which are very much angled, somewhat as in the 

 Vanessidce, but not gilt as the latter usually are, bear a 

 strong family likeness. They end anteriorly in a single 

 point : in each there is a greenish or greyish ground- 

 colour, sprinkled with numerous black dots, arranged 

 in a more or less regular manner. All are fastened to a 

 silken pad by tiny hooks at the anal extremity, and 

 further supported by a silken girdle round the anterior 

 part of the body. So supported, they pass the winter 

 not on the food-plant, but under the coping of a wall 

 or in some similar place of shelter. 



