THE FOUR-WINGED PARASITES 185 



developed into a thousand flies. Of how many flies would 

 she be the mother ? 



Do you wonder that these parasites are important ene- 

 mies of injurious insects, and are often able to check seri- 

 ous outbreaks of great crop pests ? 



The Proctotrypid Flies 



The third great group of insect parasites is that of the 

 Proctotrypid Flies. These are nearly all very minute crea- 

 tures somewhat similar to the chalcid flies. A large pro- 

 portion of them develop in the eggs of other insects, sev- 

 eral sometimes emerging from a single host egg. Many 

 of them are parasites upon parasites, and some undergo a 

 development of many larvas from one egg, as in the case 

 of some of the chalcids. 



There is one giant in this family. It is the strange 

 Pelecinus Fly pictured below. Apparently it is a parasite 

 of the white grub — the larva of the common May beetle. 

 The female Pelecinus is much smaller than the male and 

 is a very different-looking insect. 



Pelecinus Fly 



