10 BULLETIN 248, U. S. DEPARTMENT OF AGRICULTURE. 



extreme drought is detrimental to reproduction of fleas, excessive 

 rainfall also has a restraining influence. These conditions influenc- 

 ing flea abundance are dependent to some extent on the character of 

 the soil and the presence of hosts and breeding places. Sandy soil 

 is best fitted for flea breeding, as drainage is facilitated and the 

 surface is not so apt to become dried out as on many other soils. In 

 other words, it provides more uniform moisture conditions. It is 

 also probable that sandy soil is of some benefit to the flea by offering 

 more protection to the adult insect. 



The local abundance of fleas is, of course, dependent upon factors 

 mentioned in the preceding paragraphs, but in addition the abun- 

 dance of hosts, their relationship to one another, and the presence of 

 breeding places are of much importance. The abundance of rats in 

 seaports is often responsible for a large flea population, and the 

 continued destruction of the rodents often correspondingly reduces 

 the number of fleas. As has been explained, fleas often feed on 

 several different animals, and when these animals associate they each 

 contribute to the breeding of fleas. An example of this occurs in 

 the instance of the chicken flea, or " sticktight." This flea feeds in 

 great numbers on dogs and cats, and when these animals sleep in 

 and around chicken yards they and their beds are often the source 

 of great numbers of fleas which attack the poultry. Another in- 

 stance of the effect of the association of hosts and presence of 

 breeding places for fleas may be given. Often untold numbers of fleas 

 may continually infest houses and annoy the inhabitants as a result 

 of hogs, dogs, or other animals being allowed to go beneath the 

 house to make their beds. 



THE JUMPING OF FLEAS AND OTHER MEANS OF SPREAD. 



The question of the distance a flea can jump, especially in a vertical 

 direction, is important in considering isolation of man or animals 

 from them. The jumping powers of fleas are exaggerated in the 

 minds of most people. The human flea is probably the strongest 

 jumper. Mitzmain, working in California, found the maximum 

 horizontal distance this species could jump was 13 inches. He found 

 a few specimens could jump to a height of 7} inches. Five inches has 

 been recorded as the maximum horizontal jump of the Indian rat 

 flea by the Indian Plague Commission, and in experiments conducted 

 by Mitzmain 3-J inches was the greatest height to which this species 

 could jump. In other tests investigators found that the European 

 rat flea and common ground-squirrel flea (Oeratophyllus acutus) 

 could jump slightly less than 3 J inches in a vertical direction. Ob- 

 servations of the writer on the sticktight flea indicate that its jump- 

 ing power is almost nil. The legs of this species are comparatively 



