FLEAS 



(Order SipJionaptera.) 



The insects of this order, comprising all of the true fleas, 

 are all contained in a single family, the Pulicidse. They are all 

 wingless, the mouth-parts are formed for sucking, and the body 

 is compressed from side to side. The antenna are short and 

 thick, and are placed in depressions behind the simple unfaceted 

 eyes ' The metamorphosis is complete. They are the greatest 

 jumpers known in nature. The fleas are like the mosquitoes, 

 comparatively few in number of species, but very abundant in in- 

 dividuals,andwell 

 represent in struc- 

 ture the degraded 

 form which is the 

 result of a semi- 

 parasitic life. 



They prey upon 



nearly all species 



of warm-blooded 



animals, some, 



and in fact most 



species of fleas, 



passing readily 



from one species of 



animal to another. 



Very many dif- 

 ferent kinds of 



birds are infested 



by Pulex avium, 



while Pulex ser- 



raticeps occurs all a 



over the world, Fig. 112.— Pulex serraticeps. (Author's illustration. j 



191 



