410 FLEAS 



The adult fleas, according to Strickland's work on the rat flea, 

 do not become sexually mature for some days after they escape 

 from the cocoon, and copulation does not occur until this time, 

 nor, in the case of the rat flea, until after a feed of rat's blood, the 

 latter apparently acting as a stimulus to reproduction. Soon 

 after copulation the eggs begin to be laid. 



In the dog flea, Cienocephahis canis, the entire cycle from egg to 

 adult is said to be passed through in a minimum of two weeks, in 

 the human flea, Pulex irritans, in 19 days (in southern Europe) 

 and in the rat fleas in about three weeks. Ordinarily, however, 

 the life cycles occupy a considerably longer time, the average 

 being from one to three months. 



The length of life of adult fleas depends largel}^ on food supply, 

 temperature and humidity. Unfed fleas, unless allowed to bury 

 themselves in rubbish, usually die in less than a month, though 

 when buried in debris they may be kept alive many months. 

 Well fed rat fleas kept at low temperatures (about 60° F.) and high 

 humidity may live for nearly a year and a half, according to 

 Strickland's experiments. The optimum climatic conditions and 

 normal length of life probably vary a great deal with different 

 species. 



Unlike most blood-sucking insects, fleas usually feed at fre- 

 quent intervals, usually at least once a day, and sometimes much 

 oftener than this. The frequent biting is due to the fact that 

 fleas are very easily disturbed while feeding and seldom complete 

 a meal at one bite. Moreover, the capacity of the stomach is 

 not so great as in many other blood-sucking insects. The human 

 flea and some others are mainly nocturnal, visiting their hosts 

 chiefly at night, whereas others, such as the cat and dog fleas, 

 remain in the fur of the host nearly all the time. Some species 

 show a decided preference for certain parts of the body of their 

 host. 



Fleas and Disease. — Like most other blood-sucking parasites, 

 fleas are intimately connected with the spread of disease. The 

 most serious charge against them in this connection is the dis- 

 semination of bubonic plague, which as a human scourge ranks 

 with such diseases as smallpox and leprosy. In fact, few diseases 

 have ever ravaged the human race with more terrible destruc- 

 tiveness than plague when it breaks forth as an epidemic and 

 becomes rampant. It is estimated that in the epidemic of the 



