Wasps, Bees, and Ants 473 



develops on the leaf, but which after reaching full growth falls off, when the 



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Af 

 1^' 



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Fig. 665. — The giant gall of the California white oak, produced by Andricus calijornicus; 

 at right a gall cut open to show inside structure. (After Jordan and Kellogg; one- 

 half natural size.) 



wriggling of the still active larva within causes it to roll about or even spring 

 a quarter of an inch or more into the air. 



Of the rose-galls Comstock mentions 

 the mossy rose-gall, produced by Rhodites 

 ros(B, as a very common one on the sweet- 

 brier. It consists of a large number of 

 hard kernels surrounding the branch and 

 covered with reddish or green mossy 

 filaments. In each kernel is a larva. 

 The pith blackberry - gall, Diasirophus 

 nebulosus, is a common, many-chambered, 

 large, woody gall that occurs on black- 

 berry - canes. It attains a length of 3 

 inches and a width of i inch to i^ inches. 



Regarding the wonderful instinct of 

 the gall-fly, I quote the following from 

 Stratton, an English student of galls: 



"It is impossible that intelligence or 

 memory can be of any use in guiding the 

 Cynipidte; no Cynips ever sees its young, 

 and none ever pricks buds a second season, 

 or lives to know the results that follow 

 the act. Natural selection alone has pre- 

 served an impulse which is released by 

 seasonally recurring feelings, sights, or 

 smells, and by the simultaneous ripening of the eggs within the fly. 





3 



Fig. 666. — Jumping galls of the oak 

 produced by Cynips quercus-sal- 

 lalrix. (Gails on leaf of natural 

 size; at left a single gall much 

 enlarged.) 



