352 



THE STUDY OF INSECTS 



that of the preceding species but is easily distinguished by its internal 

 structure. The adult gall-flies emerge in June and early in July; they 

 are male and female; an agamic form of this species is not known. 



The giant oak-gall, Andricus calif ornicus. — This is the most com- 

 mon oak-gall of the Pacific Coast. It is very abundant on the twigs 

 and branches of the California white oaks, and during the winter, when 

 the trees are bare, it is a very conspicuous object, on account of its 

 abundance and large size. It varies in shape from globose to reniform 

 and also varies greatly in size, some of the larger ones measure more 

 than 4 inches in their greatest diameter. The outer surface of the gall is 

 white and usually smooth; the interior is more or less filled with a com- 

 pact soft material, and contains from one to a dozen larval cells. 



The mossy rose-gall, Rhodites roses. — This is a very common poly- 

 thalamous gall, which is formed on the stems of rose bushes, especially 



Fig. 596. — The mossy rose-gall. 



of the sweetbrier. The gall consists of a large mass of moss-like filaments 

 surrounding a cluster of hard kernels (Fig. 596). In each of these kernels 

 a gall-fly is developed. The galls appear early in the summer but the 

 adults do not emerge till the following spring. These are male and fe- 

 male; there is no alternation of generations in this species. 



Family Chalcidid^e 



The Chalcid-flies 



This family is a very large one for it includes many thousands of 

 species. Most of the species are very small insects and some are minute, 

 measuring not more than a quarter of a millimeter in length; some spe- 

 cies are much larger but these do not exceed the honey-bee in size. Most 

 of the species are black, with strong metallic reflections, although some 



