66 



PARASITES OF THE DOMESTIC ANIMALS 



more regularly rounded than that of the dog flea, and bears two bristles, 

 one low, in the vicinity of the maxilla, the other below the eye. 



Life History.— In their life history the fleas undergo a complete 

 metamorphosis. The eggs are oval, 0.5 mm. in length, and in color 

 pearly white (Fig. 36, a). They are deposited loosely and unattached 

 among the hairs of the host, dropping off readily during the movements 

 of the animal. The period required for the eggs to incubate may be 

 from one to four days or longer, depending much upon temperature. 



The larvae are white, elongate, apodal, and have thirteen segments, 

 each provided with bristles (Fig. 37) . They are very active and, avoiding 

 the light in every way possible, seek such shelter as is afforded by crev- 



FiG. 34. — The dog flea, anterior 

 portion of body (after Osborn, Bui. 

 No. 5, Bureau of Entomology, 

 U. S. Dept. of Agr.). 



Fig. 35. — The human flea 

 (Pulex irritans), anterior por- 

 tion of body (after Osborn, 

 Bui. No. 5, Bureau of Entomol- 

 ogy, U. S. Dept. of Agr.). 



ices in the floor, carpets, rubbish, or bedding of kennels, such material 

 containing fecal or other organic matter upon which they feed, being 

 especially favorable for their development. 



The length of the larval stage varies considerably under the influence 

 of temperature. It may be from seven to thirty days, during which 

 time there are two molts. Just before entering the pupal stage the 

 larva spins a white silken cocoon within which the pupa (Fig. 36, c) is 

 lodged (Fig. 36, b). Transformation to the fully developed imago — 

 again depending upon temperature and moisture — will occupy from 

 five to ten days. The time required for the development of the mature 

 insect from the deposited egg is, therefore, from thirteen to forty-four 

 days, with twenty-eight days as probal^ly a fair average under our 

 ordinary climatic conditions. 



Habits and Relation to Disease. — Nearly all species of fleas have 

 some one host upon which they prefer to live, but they will often live 

 and thrive upon other animals. The human flea will infest dogs and 



