72 PRACTICAL ZOOLOGY 



live in or are carried about on the bodies of other animals. Some 

 of them are harmful, such as lice, but others are beneficial because 

 they parasitize and kill other injurious insects. As a rule the 

 parasites are very small. They lay one or more eggs in or upon 

 the body of their victim, the host, and the young insect that 

 soon emerges from the egg feeds slowly upon the substance 

 within the host's body. It finally reaches the adult stage and 

 leaving the remains of its victim behind, escapes in search 

 of new prey. At the present time many insect pests, such as 

 the army worm, tussock moth, and gypsy moth, are partially 

 held in check by parasites, and the Bureau of Entomology of 

 the Department of Agriculture is making all possible efforts 

 to introduce into this country parasites from foreign lands in 

 the hope of finding some that will equal the performances of 

 the predaceous Vedalia lady beetle. 



REFERENCES 



Our Insect Friends and Enemies, by J. B. Smith. J. B. Lippincott Co., 



Philadelphia. 

 Bulletins and Circulars published by the Bureau of Entomology, U. S. 



Department of Agriculture. 



