FARMERS BULLETIN 897. 



but when excessively numerous may prove a troublesome pest to man ; 

 the human flea normally attacks man, but may be found on a num- 

 ber of other animals; rat fleas, in the absence of their usual hosts, 

 will bite man, and these fleas are the ones ordinarily responsible for 

 the inoculation of man with bubonic plague. 



Fleas of difl'erent species vary markedly in the intimacy with 

 which they are associated v/ith their hosts. Some kinds remain upon 

 host animals practically all the time. In fact, the chigoe flea nor- 

 mally buries itself in the skin of the host and there develops its 

 eggs and dies. The sticktight flea, or chicken flea, has the habit 

 of intimate association with the host, but does not bury itself in 

 the flesh of the animal. Dog fleas ordinarily remain upon the 



domestic animals 

 \^ almost continuously 



throughout their 

 existence, but are 

 not attached and 

 feed only at inter- 

 vals. The human 

 flea remains upon 

 man but little, be- 

 ing elsewhere the 

 greater portion of 

 the time. 



The life of the 

 flea has four dis- 

 tinct stages, as is 

 the case with many 

 other insects; these 

 stages are the egg, 

 larva, pupa, and 

 adult. 



A number of eggs are deposited by each adult female flea. The 

 egg laying, alternated with feeding, extends over a considerable time. 

 In most cases the eggs are deposited by the fleas while the latter are 

 on the animal host, but as they usually are not cemented to the hair 

 or feathers they fall out in the nest or resting place of the animal. 

 The eggs are cream-colored or white and ovoid. Large numbers of 

 them often may be seen on mats or cushions upon which infested dog>^ 

 or cats sleep. Especially are they easily observed when on dark- 

 colored cloths. Hatching usually takes place from 2 to 12 days after 

 deposition. 



The larva when first hatched is whitish, very minute, and (juite 

 active. (See fig. 2, larva of European rat flea.) In this stage fleas 

 are not parasitic. They depend upon various animal and vegetable 

 debris, including the excrement of the adult fleas, for food. During 



Fig. 1. — The dog floa : 

 d, adult, b, c, d, 

 (Howard.) 



fl. Egg ; h, larva in cocoon ; c, pupa ; 

 Much enlarged ; a, more enlarged 



