PLEAS. 



17 



upon man as a host, although in Europe it seems to thrive on the 

 badger, while in the United States it is commonly taken on the 

 skunk. It has also been taken on hogs, rats, and various other ani- 

 mals, but these are usually but temporary hosts and insufficient to 

 maintain the species. 



On the Pacific coast the species is responsible for practically all 

 annoyance to man due to this group of parasites. It has been found 

 to be the one concerned in nearly all cases of house infestation in 

 that section. In the Southern and Eastern States, as will be pointed 



Fig. 5. — The human flea {Pulex irritans) : Adult female. Greatly enlarged. 



(Original.) 



out later, the dog flea is more important as a pest to man than the 

 human flea. Our main interest in the human flea is on account of its 

 annoyance to man, as it is not as yet known to play any part in dis- 

 ease dissemination in this country. Nevertheless, the possibility of 

 its being an occasional carrier of plague and also that it may trans- 

 mit the infections fever kala-azar of the Mediterranean region should 

 not be lost to sight. 



Curiously enough, the human flea appears to have adapted itself 

 to the varied conditions under which man lives. It breeds freely in 

 all situations occupied by man, and in the immature stages is one of 

 the most hardy species known to science. The biology of this species, 



