i8 2 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



leaf or stem, while others, as the giant oak-gall of California, 

 are as large as one's fist. The gall-fly larvae lie in the middle 

 of the galls feeding on the abundant plant juice and pupating 

 there in the autumn when the active plant growth ceases. The 

 gall-flies issue in the following spring, biting their way out of 

 the gall by means of their stout jaws. 



The fourth, fifth and sixth groups of Hymenoptera are the 

 wasps, bees and ants. They are treated in the following 

 chapter. 



