THE CLASSIFICATION OF INSECTS 



i73 



They are especially common in dirty dwellings and in cat and 

 dog houses. With the common cat- and dog-flea the larval 

 life lasts only one or two weeks. When full grown the larva 

 usually spins a thin silken cocoon within which it pupates. 

 The adult flea issues in a few days after pupation. In a few 

 species, as the "chigoe" or "jigger" flea of the tropics, the 

 adults burrow into the skin of the host, lay eggs there and the 

 young may pass their development in a sort of tumor caused 

 by the burrowing adult. The hen-flea of the southern States 

 has the same habit of development. The rat-fleas have been 



Human-flea, Pulcx irritans; male. 



proved to disseminate the germs of plague among rats (see 

 Chapter XXIX). The commonest fleas affecting man are 

 the human-flea, Pidex irritans, and the cat- and dog-flea, 

 Ctenocephalus canis. The best way to fight them is to keep 

 rooms and the places where cats and dogs sleep thoroughly 

 clean. Flea larvae will not develop successfully in places 

 where they are often disturbed, hence much sweeping and 

 scrubbing will keep them down. The adult fleas are very 

 resistant to insecticides. 



