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 eg^ 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 



„ , .^ ,j- ^ ^V 1 ■ J Ichneumon Flies 



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 



MiCROGASTER FlIES 



One of the most abundant groups of the Ichneumon 

 Flies is that of the Microgaster Flies. These are rather 

 ^^g^«^ small insects that deposit their 

 ^^^^J^jS^^g eggs in smooth-skinned caterpil- 

 0fftBB§BBS'K^ l^i's °^ many kinds. As a rule, 

 COCOONS OF MICROGASTER cach fcmalc fly is provided with 

 Flies a pointed ovipositor with which 



she can pierce the skin of the caterpUlar 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 im- 



