Useful Insects 



175 



adult often feeds on nectar. The usefulness of this 

 class of insects is due to the fact that the young are 

 parasites. They do not secure their prey by force. 

 Instead of catching the insects and carrying them to the 

 young larvae, their eggs are deposited in the bodies of 

 their victims, and there grow into grubs. The grubs 

 either mature in the body of the hosts, or come out and 

 mature in the ground. The eggs are most often deposited 

 in caterpillars, though sometimes in the chrysalis and 



Fig. 113. A, dead "green bug," showing hole 

 from which the matured parasite emerges. The 

 top figure shows the lid still attached, but 

 pushed back; the bottom figure shows the para- 

 site emerging; B, principal parasite of the 

 spring grain-aphis or "green-bug;" adult female, 

 highly magnified. After Webster, United States 

 Department of Agriculture. 



on the adult stage, or even in the eggs. We find here 

 the same specialization in hosts that we noticed in the 

 fungi, and plant-eating insects. Each species of parasitic 

 fly rarely attacks more than one species of insect. Two 

 species (Fig. 113), of the ichneumon fly attack the 

 green bug. They thrive only during the warm weather 

 of spring, however, while the green bugs may endure 

 much cold weather. Below central Texas, the parasitic 

 flies are active at all seasons and that section has never 



