154 



Insects and Disease 



larger species, Ceratophyllus fasciatus is by far 

 the most common flea found on rats, and is com- 

 monly known as the rat flea. It occurs on both 

 the brown and the black rats Mus norvegicus and 

 M. rattus, on the house mouse and frequently on 

 man. It has also been taken in California on 

 pocket gophers and on a skunk. 



The common human flea (Pulex irritans) 

 (Figs. 108, 109), is found in all parts of the in- 

 habited world. Although we regard it primarily 

 as a pest of human beings it often occurs very 

 abundantly on cats, dogs, mice and rats as well as 

 on some wild mammals such as badgers, foxes and 

 others and has occasionally been found on birds. 



Most entomologists regard the fleas commonly 

 found on cats and dogs as belonging to one species 

 Ctenocephalus canis. Others believe them to be 

 distinct species and call the cat flea Ctenocephalus 

 jelis. So far as our personal comfort and safety 

 is concerned it makes but little difference to us 

 whether the flea that bites us is called canis or jelis 

 for they both look very much alike, and act alike 

 and the bite of one hurts just as much as the bite 

 of the other. Although cats and dogs are their nor- 

 mal hosts they are very often troublesome house- 

 hold pests, sometimes making a house almost un- 

 inhabitable. They are frequently found on rats, 



