THE PARASITES OF THE CABBAGE WORMS. 



I SHOULD not be surprised if some morning in the box in 

 which you were rearing the cabbage worms collected out-of- 

 doors when partly grown, you found only a shapeless withered 

 skin in place of a fat green worm. And beside the skin you 

 will see twenty or thirty small yellow bodies, lying in an irreg- 

 ular mass (Fig. 16). Each of the bodies, on closer view, you 

 will see are composed of fine silken threads. 



Fig. 16. — Cocoons of Cabbage Worm Parasite. 



These are the cocoons of another kind of insect. The way 

 they came where they are is explained in this wa}^ : some 

 weeks before, when the cabbage worm was only partially grown, 

 a small, black, four-winged fly (resembling Fig. 11) lit upon the 

 worm while feeding or resting on the cabbage plant, and 

 deposited beneath its skin twenty or thirty tiny eggs. 



In a few days these eggs inside the cabbage worm hatched 

 into minute footless maggots, which remained within the body 

 of the caterpillar, absorbing its life-blood. On this account 

 the maggots are called parasites. In order to grow they rob 

 another creature of its life. 



The parasitic maggots finally become full-grown in this lar- 

 val stage of their life. Then, all acting at the same time, they 



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