FLEAS. 3 



monly on certain hosts, but they are not at home on these and would 

 probably not live long or reproduce if made to feed on them ex- 

 clusively. This class of hosts usually becomes infested by being 

 closely associated with the true host of the fleas, as, for instance, in 

 case of a rat entering a squirrel burrow or a carnivorous animal de- 

 vouring a flea-infested rodent and thus getting the insects upon its 

 body. Such hosts are usually spoken of as accidental or temporary. 

 While infestations of this kind are seldom of importance to the host 

 animal from the standpoint of direct injury, they may have a vital 

 influence by transmitting disease and may also have an important 

 bearing on control. As a result of this habit of fleas of clinging to, 

 or temporarily feeding on, hosts which are not necessarily congenial, 

 long lists of species of fleas accredited to a single kind of animal or 

 bird are often found. For instance, more than 20 species of fleas 

 have been taken on common wharf rats. 



BITING HABITS. 



The sensation produced by the biting of a flea is well known to 

 most persons. The annoyance, however, is partly produced by the 

 movements of the insect and by the mental unrest caused by the 

 knowledge that fleas are present beneath the clothing. The effect of 

 flea bites on man is discussed further on page 16. With very rare 

 exceptions, adult fleas partake of no food other than the blood of 

 warm-blooded animals, and it appears that reproduction never takes 

 place until the fleas have partaken of such blood. 



The mouth parts are well adapted to piercing the skins of their 

 hosts and sucking up the blood. The essential piercing organ con- 

 sists of three slender parts. A groove along the inner sides of two 

 of these, the mandibles, with the closely applied third, forms a chan- 

 nel through which the salivary fluid is forced into the wound and 

 through which the blood is pumped into the body. An idea of the 

 structure of the mouth parts may be gained by referring to figure 1, 

 e and g. 



Most speeies are easily disturbed when feeding, and this accounts, 

 in part at least, for the frequency with which a single flea may bite. 



With the exception of the " sticktight " flea and certain of its rela- 

 tives, fleas do not remain attached to their hosts for long periods. The 

 amount of time spent off the hosts seems to vary much with the spe- 

 cies. Normally the adults feed every day and possibly oftener, but in 

 the case of interrupted meals, as has been mentioned, they may bite a 

 great many times during a day, and some species, such as the cat and 

 dog fleas, probably remain on the host almost continuously, feeding 

 at very frequent intervals. A great many fleas are nocturnal. These 



