102 THE FLEA [CH. 



The species of flea commonly found on rats are 

 five in number, and the readiness with which they 

 bite human beings has been carefully studied. 



1. Xenopsylla cheopis. This is the oriental rat- 

 flea first described by Mr Charles Rothschild from 

 specimens collected in Egypt. The true home of 

 this flea appears to be the Nile valley, where it may 

 be found in plenty on various hosts. Many of these 

 are desert animals and the flea shows a preference 

 for rodents. Having been distributed all over the 

 world by rats, it now occurs, occasionally, in all warm 

 climates. It is the common rat-flea of the tropical 

 and sub-tropical world. In India it often happens 

 that the whole of the fleas collected from rats prove 

 to be of this species. But it cannot, apparently, 

 flourish in cold countries. In the warmer temperate 

 zones, such as the Mediterranean and Australian sea- 

 ports, it occurs in varying proportions according to 

 the time of year. The numbers decline with cold 

 weather. It readily bites man and is more active 

 than any other flea in the transmission of plague. 

 For this reason it is sometimes spoken of as "the 

 Plague-flea." It is a smaller and a lighter coloured 

 insect than the human flea. 



2. Ceratophyllus fasciatus. This is the common 

 European rat-flea, It is the rat-flea of the temperate 

 as opposed to the hot countries of the world. It 

 is commonly found on black and brown rats in the 



