162 SAWFLIES, ICHNEUMON-FLIES, WASPS, ETC. 



number of eggs, sometimes more than sixty, in one 

 caterpillar of the large Cabbage Butterfly. Here the 

 maggots hatch and feed, avoiding by instinct such 

 parts as the consumption of would be a fatal loss, 

 firstly, to the host, consequently to the guest. The 

 containing caterpillar — the live food, that is — mean- 

 while feeds and grows, not only until it attains its 

 full size, but it may often be known from uninfested 

 ones by its swollen appearance. It has not, however, 

 power to turn to the chrysalis state : when the time 

 for this comes, the maggots within pierce its skin, and 

 each one spins for itself a small cocoon of yellow silk, 

 in which it goes through its changes to the complete 

 insect by the side of the dead body of the exhausted 

 caterpillar. These little Ichneumon Flies are one of 

 our protections against great increase of the cater- 

 pillars, and the small silken cocoons, which are easily 

 seen when they lie together in masses on Cabbage 

 leaves, should never be destroyed. 



Pig. 126. — 1 — 4, Gieen-vcined White Butterfly ; 5 and 6, Ichneumon 

 Fly {Hemiteles melanarim), magnified, with nat. size. 



Another kind of small Ichneumon Fly (Hemiteles 

 melanarius) preys in the same way, by means of its 

 maggots, inside the chr3^salids of the Green-veined 

 Cabl)age Butterfly. These infested chrysalids may be 

 known by their dark brown colour, and should never 

 be destroyed, as each one is a case — a package, so to 

 say — full of checks to a troublesome crop -prey er. 



