THE CLASSIFICATION OF INSECTS 



181 



smallest insects known to others two inches or more in length. 

 Some of these minute parasites lay their eggs within the eggs of 

 other insects, and their larvae live their whole lives in the con- 

 tents of these host eggs, but most Hymenopterous parasites 

 deposit their eggs on the skin of the larvae or nymphs of other 

 insects, especially on caterpillars. The parasite larvae, on 

 hatching, bore their way through the skin into the host body 

 and remain there, feeding on the blood lymph and perhaps on 

 other body tissues. The host dies, but 

 usually not until the parasites have com- 

 pleted their larval life and have changed 

 to pupae either within the host's body, or 

 have issued from it and pupated outside. 

 Parasitized caterpillars are often able to 

 pupate, but from their pupa there issues, 

 not a moth or butterfly, but many of the 

 little four-winged parasites. These fly 

 freely about, mate, and then deposit their 

 eggs on the body of other hosts. 

 , A few members of this group are not 

 parasites but gall-makers. Among these 

 an important kind is the curious small fig- 

 wasp (Blastophaga) by which the Smyrna 

 figs are cross-pollinated and made to set 

 seed and thus to become especially palata- 

 ble. The fig- wasp has been introduced from Asia Minor into 

 California, and has greatly added to the value of California 

 figs. 



Third, the family Cynipida or gall-flies, some of which are 

 parasites, but most of which thrust their eggs, by means of a 

 sharp ovipositor, into the leaves or green stems of oaks, roses 

 and a few other plants, so that the hatching larvae find them- 

 selves surrounded by rich plant food. The presence of the 

 larva stimulates the plant to a vigorous production of new 

 tissue about it, which takes on the form of a gall of definite 

 shape. These galls are different for different species of gall- 

 flies, and for different species of plants, and present a host of 

 curious shapes. Some look like tiny seeds or papillae on the 



FIG. 85. Ichneu- 

 mon fly, Pimpla con- 

 qidsitor, laying egg in 

 cocoon of American 

 tent-caterpillar moth. 

 (About natural size; 

 after Fiske.) 



