CHAPTER XIV 



Order Siphonaptera (Aphaniptera) : Fleas 



Gr. o-t'^ft))/ = sucking tube ; a-Trreyoo? = wingless ; a0ai'>;$' = in- 

 visible ; -TTTepov = wing. 



The Siphonaptera, or Fleas, are laterally compressed, wing- 

 less insects, with mouth-parts formed for piercing and sucking, 

 and they undergo a complete metamorphosis in the course 

 of their post-embryonic development. The head is broadly 

 articulated to the thorax, and all three segments of the 

 thorax are distinct and independent. Fleas have often been 

 classed as a suborder of Diptera, but this arrangement can 

 not be supported. 



Fleas are active parasites of mammals and birds. Some 

 fleas will suck blood from any warm-blooded animal indis- 

 criminately, but the majority either restrict themselves to 

 one definite species of animal (host), or have a decided 

 preference for one species and attack other species with 

 some reluctance. In one family {SarcopsyllidcB or Dermato- 

 philidcB) the females, besides sucking blood, eventually attach 

 themselves to their host as fixed parasites, embedding them- 

 selves in its skin when they are pregnant. 



Fleas may act as direct mechanical "carriers," and also 

 as necessary intermediaries of other parasites of their host. 

 Thus the common dog-flea, and the common European rat- 

 flea are known to harbour the cysticercus of certain tape- 

 worms of their respective hosts, and the trypanosome of 

 the rat has been shown to pass through certain stages of its 

 developmental cycle in the European rat-flea. But the great 

 importance of fleas from the medical officer's standpoint is 

 due to the part that these insects play as carriers of the 

 plague-bacillus among rats and other rodents, and from 

 these to man. 



