THE FOUR-WINGED PARASITES 177 



illustrated on page 174. The egg develops within the 

 body of the host into a white footless maggot that soon 

 matures as a larva and changes to a pupa, which in turn 

 shortly changes into an adult Pimpla. 



Many of the Ichneumon Flies deposit their eggs within 

 the burrows of larvae that bore in the stems of herbaceous 

 plants or the bark or trunks of shrubs and trees. In such 

 cases, it evidently would be difficult for the mother parasite 

 to find precisely the location of the burrowing larva, so she 

 simply deposits her egg within the burrow of the latter, 

 and the little larva that hatches from this egg is generally 

 provided with some method 

 by which it is able to reach 

 its victim. Instead, however, 

 of developing on the inside 

 of its host, it usually simply 

 attaches itself to the skin and 



sucks its lifeblood from the outside. It finally kills the 

 host, becomes full-grown as an Ichneumon larva, and changes 

 first to a pupa, and a little later into an adult fly that is able 

 to eat its way out through the bark of the plant. 



MlCROGASTER FLIES 



One of the most abundant groups of the Ichneumon 

 Flies is that of the Microgaster Flies. These are rather 



small insects that deposit their 

 eggs in smooth-skinned caterpil- 

 lars of many kinds. As a rule, 

 COCOONS OF MICROGASTER each female fly is provided with 

 a pointed ovipositor with which 



she can pierce the skin of the caterpillar to insert her eggs 

 within its body. These eggs shortly hatch into tiny mag- 

 gots that develop at the expense of the tissues of the un- 



