8 THE FLEA [CH. 



Observations made on the development of the 

 dog-flea (Ctenocephalm cams) in India show that 

 eggs laid on October 17 hatched on October 19. The 

 larva spun its cocoon on October 25 and the mature 

 flea emerged on November 2. In Northern Europe 

 the human flea takes about four weeks in summer 

 and six weeks in winter to pass through its meta- 

 morphosis. 



Unlike many parasitic insects, fleas do not con- 

 stantly pass their time upon the bodies of their 

 victims. The greater part of their life is probably 

 spent on the ground, in the house, or nest, of the 

 mammal or bird which serves them with blood. In 

 this respect there is considerable difference in the 

 habits of different species of flea. Some attach 

 themselves to an animal and actually burrow into 

 the skin. These are the most parasitic species. 

 Some only come to feed and leave to lay their eggs. 

 Many probably do not suck blood more than once 

 in their lives. 



An animal which harbours fleas and which 

 nourishes the adult insect with blood is called a 

 host. No fleas are more than what is called 

 temporary parasites; which means that they pass 

 but a portion of their lives on their hosts and 

 frequently take occasion to hop on and off. All 

 fleas, apparently, go from host to host. The labours 

 of diligent collectors have proved that the great 



