362 



SANITARY ENTOMOLOGY 



With the Indian rat flea the period was greatly lengthened when the 

 mean temperature fell below 65° F., human flea below 50° F., and the 

 European rat flea below 40° F. In cooler climates the winter is probably 

 passed in this stage but in warmer countries adult activities never cease. 



Fig. 65. — The dog flea {Ctenocephalus canis): a, Egg; b, larva in cocoon; c, pupa; d, 

 adult; e, mouth parts of same from side; f, antenna; ff, labium from below; b, c, d, 

 much enlarged; a, e, f, g, more enlarged. (From Howard.) From U. S. Dept. 

 Agr., Bull. 248, fig. 3. 



The adult fleas often remain in the cocoons for weeks and emerge when 

 disturbed. 



Life Cycle. — The cycle is completed under favorable conditions in 



Fig. 66.— The human flea, Piilex irritans: Adult female. Greatly enlarged, (Bishopp.) 



one to four weeks, but it may extend to one and one-third j^ears in 

 extreme cases. 



Length of Life of Adult Fleas. — A knowledge of the length of life of 

 the adults is of much importance in relation to control measures and 

 disease dissemination. Under cool, moist conditions Bacot found the 

 human flea to live 125 days, the European rat flea 95 days, the dog flea 



