THE LIFE HISTORY AND CONTROL OF FLEAS 361 



the outset that all fleas are dependent upon blood for their existence. 

 There is considerable variation in the degree to which certain species are 

 restricted as regards their host, and we ohould not go too far in drawing 

 conclusions as to whether certain species will not feed on certain hosts 

 as our judgment is based usually on a comparatively small number of 

 experiments under more or less artificial conditions, or upon examinations 

 of a small number of host species, often in restricted districts. 



Fleas pass through four distinct stages — egg, larva, pupa (in a 

 cocoon), and adult. The eggs are readily seen with the naked eye, espe- 

 cially when on a dark background. Most of them are deposited by the 

 females while the latter are on the host. They fall off the host, mostly 

 dropping in the bedding material where they hatcli in from two to twelve 

 days. This is responsible for a concentration of the adults about the 

 sleeping places of the hosts, and favors them b}' being within easy reach 

 of the hosts, both old and young, and also in supplying the larva? with 

 the partially digested blood excreted by the adult fleas, for food. The 

 number of eggs laid varies greatly according to species, availability of. 



Fig. 64. — Larva of the European rat flea, Ceratophyllus fasciatus. Greatly enlarged. 

 (Bishopp.) From U. S. Dept. Agr., Bull. 248, fig. 3. 



food for adults, etc. Bacot, of the Lister Institute, has counted as 

 many as 448 eggs deposited by a female human flea. Comparatively 

 few are deposited each day but the egg laying may be extended over many 

 weeks. 



The Larvae. — The larvae are whitish, legless, and eyeless maggots, dis- 

 tinctly segmented and provided with numerous hairs (fig. 64). They 

 are usually less than one-fourth of an inch in length when grown, and quite 

 active, disappearing quickly in breeding material. Larvcie of some of 

 the larger species may considerably exceed this length. They are to be 

 found in the dust in which vegetable and animal particles are mixed. 

 The larval stage is extremely variable, mostly depending on temperature, 

 abundance of food, and degree of moisture and humidity. The length of 

 this stage has been found to range from one to twenty weeks. Under, 

 favorable conditions from one to three weeks may be taken as the usual 

 length of the period. 



The Pupa. — All flea larvae spin cocoons in which the pupa is 

 formed. These are oval and not easily seen on account of the numerous 

 particles of dust, sand, etc., which is woven in or stuck to the silken 

 cocoon. This stage ranges from a week to nearly a year. The extreme 

 long periods were observed by Bacot to take place only in cool weather. 



