FLEAS 



151 



Fig. 46. — Larva of a flea, above; 

 cocoon, below, much enlarged. 



ready, after feeding, to deposit eggs for another genera- 

 tion. Under the most favorable conditions a generation 

 of fleas may be produced in almost two weeks. It is 

 probable, however, that a 

 longer time is needed under 

 most conditions. 



Simons, who reared some 

 cat fleas from the eggs, 

 found that the eggs hatched 

 in a little over two days and 

 that the larvae became full 

 grown in seven days. They 

 then spun their cocoons, and 

 after lying quietly in them 

 for eight days more, during 

 which time they changed to pupa?, came forth as adults. 

 Thus it took seventeen days for the development of a 

 full generation. 



Howard relates that in Washington in several rearings 

 of the cat and dog fleas the eggs hatched in from two to 

 four days, the larva? attained their growth in from seven 

 to sixteen or twenty days, and the pupal state consumed 

 from five to fourteen days. Here, again, we see that a 

 single generation may be produced in a little more than 

 fourteen days. Other observers give the period of de- 

 velopment as 4 to 6 weeks and 9 to 10 weeks for the 

 human flea. Evidently the period varies with the tem- 

 perature and other environmental factors. For example, 

 in the colder season, the pupal stage of the human flea 

 may occupy as long as thirty-four days. 



The following table compiled by Mitzmain shows the 

 cycle of development of fleas in different countries. 



