THE GALL-FLIES 



(Super-family Cynipoidea.) 



To this group belong the true gall-flies, as well as certain 

 insects which are inquilines, or gall-fly guests, and also certain 

 forms which are true parasites. Although we call the Cynipoids 

 the true gall-flies, there are many other insects which make galls, 

 such as some of the two-winged flies of the families Cecidomyiidae 

 and Trypetidae, cer- 

 tain caterpillars, a few 

 Chalcis flies, and a few 

 beetles, as well as cer- 

 tain mites and scale 

 insects. Certain of the 

 oak galls formed by 

 Cynipoids were early 

 used in the manufac- 

 ture of ink, and later for 

 tannin, so that when 

 one speaks of gall- 

 flies these creatures 

 are always thought of. 

 They are small dark Fig. 27. Cynips spongifica. (After 



colored four-winged flies, at once distinguished from their close 

 allies by the venation of the wings and the structure of the thorax, 

 as pointed out in the analytical table. 



Those which make galls lay their eggs in the tissues of the 

 growing plant, and the larvae when hatched feed upon the plant 

 cells and their contents. A very slight gall deformation may 

 result, but in the majority of cases there is a rapid growth of 

 plant-cells and a curious enlargement of variable shape which is 

 called a gall. 



The nature of the gall has long been a disputed point. It 

 was at first thought that it was a purely vegetable growth and 



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