182 INSECTS 



term Pupipara, or those that give birth to pupae. They 

 are usually active, flattened, brown or yellow flies, 

 with small head and rounded abdomen. Some of them, 

 infesting birds of prey, fly actively, while others, like 

 the "sheep tick," are wingless, although not there- 

 fore inactive. They are called pupipara because the 

 egg hatches within the body of the female and the 

 larva attains its entire growth before being extruded, 

 ready to pupate. Of course this means a very slow 

 rate of reproduction, since the number of young matured 



FIG. 82. A louse fly, Olfersia species. 



at one time cannot be great; but, on the other hand, 

 it is also a safe rate, because the larvae run few dangers 

 during their early life, and the infant mortality is not 

 very high. Nestlings become infested from the mother 

 bird, and the flies are quite active enough to make 

 short flights from the host and back again when neces- 

 sary to escape an especially vigorous hunt. When 

 the host dies or is killed the parasites leave it at once, 

 and seek shelter on any living thing in the vicinity. 

 "Sheep ticks" which, as already indicated, are 

 wingless, do really look very much more like ticks 

 than like flies; their long mouth parts, small thorax, 

 long legs and round flattened abdomen giving them 



