CHAPTER XXXIII 



THE STUDY OF GALLS FAIRY FLIES 



THE STUDY OF GALLS 



AN excellent opportunity of studying the relationships between 

 certain insects and particular plants is given by galls. In the 

 lesson which has gone before, the common marble gall has been 

 examined, and it has been suggested that the insects which form 

 or inhabit it should be collected by keeping specimens in small 

 wide-mouthed bottles. There are, however, very many other 

 structures produced by plants owing to the activity of similar 

 insects and also of mites and two-winged flies. Leaving the latter 

 on one side, we might 

 point out that the 

 oak tree from which 

 the common gall is 

 obtained, is extremely 

 subject to this and 

 to a large number of 

 others. Its leaves, 

 buds, roots, and even 

 flowers, respond to 

 the attacks of various 

 four-winged insects. 



FIGURE 229. A Marble Gall-fly. 



Several kinds of galls 



which from their 



shape have been likened to silk buttons and to coins, or which are 



120 



