RAT AND SQUIRREL FLEAS 417 



mitter of bubonic plague, though its preference for dogs or cats 

 would preclude a frequent occurrence of this. 



Rat and Squirrel Fleas. — The various species of rat and squir- 

 rel fleas are only accidental parasites of man. They readily at- 

 tack him if opportunity offers but do not remain adherent to him 

 as they do to their normal hosts. If it were not for their enormous 

 importance in the spread of bubonic plague, they would hardly 

 need special consideration. 



From its intimate connection with the spread of bubonic 

 plague, the Indian rat flea, Xenopsylla cheopis (Fig. 177), is of 

 prime importance. Though other members of the genus are 

 confined to Africa and Asia, this species has now a world-wide 

 distribution, having accompanied its normal host, the rat, to all 

 warm seaports in both the Old and the New World. It is a 

 rather short, stout flea, resembling the human flea in the absence 

 of combs. Although the normal hosts of Xenopsylla cheopis are 

 rats of various species, the domestic habits of these rodents 

 bring the fleas into close association with man, and they will 

 readily feed upon him if hungry. Furthermore, deRaadt has 

 recently demonstrated that these fleas do not remain constantly 

 in the fur of their normal hosts, but that 80 per cent drop off in 

 the course of 48 hours. This species is not migratory and sel- 

 dom reaches anyone but the inhabitants of the house in which its 

 host occurs, unless carried by the rats themselves. Swellen- 

 grebel states that in Java this flea will willingly bite man on the 

 first day of fasting. In many tropical countries the Indian rat 

 flea is the commonest flea found in houses; in Egypt 96 per cent 

 of fleas caught in plague-infested houses were of this species. 



The European rat flea, CeratophyUus fasciatus, is a species 

 having habits quite similar to those of Xenopsylla cheopis. It 

 replaces the latter species in temperate climates except in sea- 

 ports, where the Indian rat flea is often more common. The 

 common rat flea of China and Japan is Pygiopsylla ahalce. The 

 larvae of C. fasciatus develop best under cool humid conditions 

 in an abundance of rubbish. Strickland, who has worked out 

 the biology of this flea in detail, found that it would actually 

 attack man in preference to rats, although a feed on the blood of 

 rats seemed to be necessary before any eggs were laid. Another 

 species of the same genus, C. gallinoB, attacks chickens in Europe, 

 and has been introduced into several parts of the United States. 



