FLEAS. 



13 



The Indian rat flea has been found to be by far the most im- 

 portant in plague transmission in India, and this species is now 

 widely distributed throughout the Tropics and in seaports which 

 have direct trade with the Orient. At the present time this species 

 is abundant in parts of the seaport cities on the Pacific and Gulf 

 coasts of the United States. Away from the water front its place 

 as a rat parasite is largely taken by the European rat flea (0. fasci- 

 atus Bosc.) and the mouse flea (Leptopsylla musculi Duges). The 



Fig. 2. — The European rat flea (Ceratophpllus fasciatus) : Adult female. Greatly enlarged. 



(Original.) 



human flea is common in many parts of the country, and the squirrel 

 fleas mentioned are abundant on ground squirrels (Oitellus beecheyi) 

 in the western part of the United States. All of these fleas have 

 been found to bite man and will feed on rats. The adult European 

 rat flea is illustrated in figure 2, the larva of this species in figure 

 3, and the cocoon in figure 4. 



As has been stated, plague always occurs among the rodent popula- 

 tion before any number of cases develop in man. The rats in a 

 plague-free community usually receive their initial infection from a 

 diseased rat which has been imported from some plague center. This, 



