HYMENOPTERA 



373 



Cabbage Caterpillar (Microgaster glomeratus), which had lain concealed 

 as pupa in the so-called " egg." Now, how did the pupa get there? If 

 we visit a cabbage-garden we may, if we are fortunate, see the fly at 

 work. It has settled upon a caterpillar in order to "infect" it with a 

 number of its eggs; for the larvae of the ichneumon fly are parasites 



which live inside of the caterpillar. To 

 convey its eggs to their destination, the fly 

 is provided at the end of its abdomen with 

 an ovipositor i.e., a tube with which it bores 

 an opening into the body of the caterpillar, 

 and through which it conveys its eggs into 

 the interior of the latter. The white maggots 

 which arise from the eggs live on the 

 tissues of their hosts, and finally break 

 through the body walls of the latter in order 

 to spin a cocoon around themselves and enter 

 the pupa stage. These pupae form the so- 

 called caterpillar's 



77 e.W. 



CHNETJMOX FLY OF CABBAGE CATERPILLAR. 



R.S.', caterpillar being stung by an ichneumon fly ; R.M., cater- 

 pillar with maggots bursting forth from its body and enter- 

 ing pupa stage; R.P., caterpillar surrounded by pupse ; 

 S., ichneumon fly; M., maggot ; P., pupse (the last three 

 figures magnified). 



Other species 

 of ichneumon flies 

 deposit their eggs in 

 other insects, in their 

 larvae, pupae, or even 

 eggs. Some, with 

 their boring instru- 

 ment, even bore into 

 wood to the depth of 

 half an inch or more 

 in order to get at the 

 bore - worms in the 

 interior of the trunk. 

 Since any insect 

 once infected by 

 these eggs is doomed 

 to perish, we must 

 regard the ichneu- 

 mon flies as impor- 



tant helpers in the destruction of numerous insect pests. 



2. We are all familiar with the galls of oak-leaves, which are about 

 the size of a cherry and of ruddy colour. If one of these be opened in 

 autumn, a small black fly, the Oak-gall Fly (Cynips quercus folii) will 

 be found inside, to which the gall owes its origin. While the leaf was 



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