RELATION TO OTHER ANIMALS 165 



There are many other kinds of fleas and they infest 

 almost every sort of animal capable of affording them 

 shelter; but there is a very general agreement in life 

 history and in the character of the methods to be used 

 in their control when control becomes a matter of im- 

 portance. Some further word concerning these insects 

 as carriers of disease will be found in a subsequent 

 chapter, where also the closer relation of those fleas 

 that occasionally occur in our houses is more fully 

 elucidated. 



Fig. 71 



Among the true flies there are a great number of 

 species that prey upon vertebrate animals, and they 

 do this in two ways: either by feeding upon them in 

 the adult stage alone, or by actually living upon them 

 in early stages, and thus becoming true parasites. As 

 the flies are among the most recent of insects, so their 

 relations to the vertebrates, the most recent develop- 

 ments in the higher animals, are also most close. 



The simplest form of relationship is that afforded 

 by the various blood-sucking flies — the mosquitoes, 

 gnats, midges, horse-flies, stable flies and others allied 

 to them. In all these species the mouth structures 

 are developed into a series of long slender lancets 



