Wasps, Bees, and Ants 



471 



"oak-apples." One of these is the fibrous oak-apple of the scarlet oak, 

 i to 2 inches in diameter, produced by the gall-fly Amphibolips coccinea. 



FIG. 661. Galls on leaf of California white oak. (Natural size.) 



This gall is distinguished by having a small hollow kernel in the center of 

 the gall, in which 

 the single larva lives, 

 the space between 

 the kernel and the 

 dense outer layer of 

 the gall being filled 

 with fibers radiating 

 out to the surface 

 from the kernel. The 

 spongy gall of the red 

 and black oak, made 

 by Amphibolips 

 spongifica, has the 

 space between kernel 

 and outer wall filled 

 by a porous, spongy 

 mass. In the "emp- 

 ty oak-apples," the 

 larger one of the 

 scarlet and red oaks, 

 Holcaspis inanis, 2 

 inches or more in 

 diameter, and the 

 smaller, of the post- 

 oak, H. centricola, f 

 inch or less in diam- 

 eter, the space be- 

 tween kernel and 

 outer wall contains 

 only a few slender silky filaments which suspend the kernel in place. The 



FIG. 663. Fio. 662. 



FIG. 662. Galls on twigs of California white oak; upper figure, 



a gall split open longitudinally. (Natural size.) 

 FIG. 663. Galls on leaf. (After Jordan and Kellogg; natural 



size.) 



