PLEAS AND THEIR CONTROL. 5 



their growth the skin is shed two or three times, and between four days 

 and several months after hatching a silken cocoon is spun, and in 

 this the larva transforms to the pupa or resting stage. 



The insect remains within tlie cocoon for a period which may range 

 from three days to more than a year. 



The complete life cycle of members of this group of insects may be 

 passed in as short a period as 17 days, but during cool weather or 

 under adverse conditions the total period from egg to adult may 

 extend considerably over a year. 



LENGTH OF LIFE OF THE ADULT. 



The length of life of the mature flea varies much as between differ- 

 ent species and under different atmospheric conditions. During hot, 

 dry weather, and when no animals upon which to feed are present, 

 the duration of life may be ex- 

 tremely short — from two to five 

 days. When allowed to feed on 

 blood, which is the only food 



taken bv the adults, they may live ^i^- 2.— The European rat flea : Larva. 

 „ " , 1 , 1 j_ Greatly enlarged. 



from a month to almost a year. 



During summer probably the average longevity of the human flea 

 without food is about two months, of the dog flea somewhat less, 

 and of the sticktight flea still less. 



ABUNDANCE OF FLEAS, WITH RELATION TO SEASON, CLIMATE, 

 AND OTHER CONDITIONS. 



In the northern part of the United States nearly all fleas pass the 

 winter in the immature stages, while in the more southern latitudes 

 some of them are present on hosts throughout the winter months. In 

 general, however, these insects are never as abundant during winter 

 and spring as they are in summer and fall. In the extreme Southern 

 States this is not always true, as much trouble from the human, dog, 

 and sticktight fleas has been observed to occur in late spring or early 

 summer when rains were frequent and the humidity high. 



Rainfall and the amount of moisture in the atmospliere have much 

 to do with flea breeding. As a rule rainy summers are productive of 

 outbreaks of fleas, and extremely hot, dry weather tends to check 

 their breeding. The larva and pupa require a certain amount of 

 moisture for successful development, and the adults live longer when 

 a proper degree of moisture is present. It would be erroneous, how- 

 ever, to infer from this that fleas require very moist places in which 

 to breed ; in fact excessive moisture- in the breeding places is as det- 

 rimental as is excessive dryness. This sensitiAonoss to excessive mois- 

 ture can be utilized in remedial work, as will be pointed out later. 



