ENTOMOLOGY IX OUTLINE HYMENOPTERA 111 



Family Cynipidse (Gall-flies). In this family we have one of the 

 mysteries of the natural world. Here we have a minute insect, in 

 some cases almost microscopic in size. This insect will puncture a 

 twig or leaf of a tree, and at once the whole character of the part so 

 punctured is changed. In the oaks, for instance, we see galls known as 

 oak apples, and often they are as large as big apples, and these are 

 formed for the purpose of supplying sustenance to the tiny maggot of a 

 gall-fly. What kind of fluid is injected to cause this change? It cer- 

 tainly is wonderfully powerful, as the amount injected must be so 

 infinitely small as to be past our comprehension, for it is but a part of 

 the insect and this is not large enough to be noticed. More than this, 

 each species creates a special kind of gall, and an entomologist can tell 

 what species of insect did the stinging by the shape, color, and general 

 appearance of these strange swellings. Now, how is it that the plant 

 will accommodate its growth to the peculiar requirements of each one 

 of the different species of these minute insects? 



It must not be understood, however, that all the members of this 

 family are gall-makers, or that there are no galls caused by other 

 insects. In fact many of the other orders have gall-makers, as the 

 aphids, the mites, etc.; but there is this difference: in other galls there 

 are external openings, while in the galls made by members of this 

 family they are closed and contain the larvae of the insect until they 

 have attained their growth. In some cases the insect goes through its 

 transformations within the gall, and in others it makes its escape and 

 changes in the earth. 



Family Ichneumonidse. We have now come to a family of especial 

 interest to the fruit-growers and farmers of California as well as else- 

 where, for in the Ichneumonidse are found the greater number of our 

 beneficial insects; that is, they are of benefit to us, as they prey upon 

 species which devour and destroy our vegetable products. It is to this 

 family that Swift's oft misquoted lines apply: 



"Naturalists observe, a flea 

 Hath smaller fleas that on him prey, 

 And these have smaller still to bite 'em, 

 And so proceed ad infinitum." 



It should be borne in mind that there are two classes of beneficial 

 insects, the parasitic and the predaceous. In the latter the insect 

 pounces upon his victim wherever he catches him, that is, if he happens 

 to be hungry, and devours him on the spot. The parasitic insects, 

 however, have a neater way of doing business. In their proceedings 

 they are not so coarse as the predaceous varieties, although they 

 accomplish their work more effectively. They attach themselves early in 

 life in fact, the mother usually brings about the match and, once 

 attached, they remain until there is nothing left of their victim worth 



