RELATION TO OTHER ANIMALS 183 



a peculiarly spider-like appearance. They are some- 

 times very abundant on sheep, and find no difficulty 

 in getting on to new animals because of the habit of 

 congregating into dense masses, peculiar to their host. 

 The body of these flies is very tough and leathery, and 

 I am informed by those who handle the raw hides 

 that they will survive all the preliminary handlings, 

 cleaning and soakings which the pelts undergo before 

 being denuded of wool and prepared for tanning. 

 Herders know of a great variety of "dips" useful 



FIG. 83. Sheep tick, Melophagus FIG. 84. A bat tick, 



ovinus. Nycteribia. 



against these insects and "dipping" is a regular prac- 

 tice wherever sheep are raised in any numbers. 



The extreme development in this direction we find 

 in the bat ticks, which are even more spider-like than 

 the sheep tick and have similar habits, while infesting 

 a much-shorter-haired animal. It is distinctly curious 

 that while there are many species of these louse flies 

 among birds, there are only a few, very aberrant forms, 

 that have adapted themselves to live on four-footed 

 animals. 



We find, then, that among the insects there are foes 

 to almost all kinds of vertebrates and that they are 

 not at all despicable foes. While the death of the 

 animal attacked is never sought as a prime object, 



