Wasps, Bees, and Ants 473 



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



FIG. 665. The giant gall of the California white oak, produced by Andricus calif ornicus; 

 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 

 rosce, 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, Diastrophus 

 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 

 Cynipidse; 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. 



FIG. 666. Jumping galls of the oak 

 produced by Cynips quercus-sal- 

 tatrix. (Galls on leaf of natural 

 size; at left a single gall much 

 enlarged.) 



