376 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



have become infected with the plague, and the Government is 

 now waging a war against them in order that the disease may 

 not be kept alive in them and again become epidemic among rats 

 and man. 



There are four species of fleas occurring in the United States 

 that are commonly found on rats. Two of these are also 

 common pests of man, and the others do not hesitate to bite 

 man when they have a chance, so that all may transmit the 

 plague from diseased rats to human beings. The cat and dog- 



FIG. 165. Human-flea, Pulex, irritans ; female. 



size.) 



(Twenty times natural 



flea, Ctenocephalus canis, is probably the most common of them. 

 It occurs in all places where cats and dogs are kept, and is often 

 more common in houses and a worse pest than the human-flea, 

 Pulex irritans, which is always a troublesome and persistent 

 biter. The common rat-flea of the United States, Ceratophyl- 

 lusfasciatus, and the Indian rat-flea, or plague-flea, Xenopsylla 

 (Lamopsylla) cheopus, are not so troublesome to man. 

 As fleas breed in the dust under the carpets, in the cracks of 



