FLEAS 75 



great variety in the feeding habits of even closely related species of 

 fleas. Some tend to take short frequent meals, others long feeds at 

 considerable intervals. Some, like human beings, lose their appetites 

 in hot weather. Again, one species will bite immediately it comes into 

 contact with the host, and another will wander about trying here and 

 there before it finally settles down to feed. 



The tropical rat flea is a wary flea and is easily disturbed, but on the 

 other hand it will try again and again to get going, whereas Xenopsylla 

 astia, a closely related species, if once put off or distracted, temporarily 

 refuses to bite. 



It is true that most fleas are not so closely bound to their host as are 

 the feather hce, but although they are in a sense free they have little 

 or no possiblity of actively searching for a bird, and luck must often 

 play a considerable part in finding one. It is therefore fortunate for the 

 flea that it is endowed with the power of fasting for considerable 

 periods. Nevertheless, it must be the fate of a large proportion of bird 

 fleas to hatch out in a nest long after the birds have gone, and to perish 

 miserably without the hope of ever tasting blood. 



Little is really known about the senses of fleas, but it appears that 

 where the response to a host is involved they only function when the 

 animal is at close quarters. For example, if hungry rat fleas are intro- 

 duced into a cage with a rat, they do not, as would be expected, make 

 a bee line for it. Instead they wander about in an aimless manner until 

 their random movements bring them within a few inches of the host. Only 

 then will they make directed efforts to reach the animal. Nevertheless 

 in practice this method is evidently rather effective, for if the cage is 

 opened after a few hours, most if not all of the fleas will be found on the rat. 



During the Plague Commission's investigations in India and Egypt, 

 guinea-pigs were sometimes liberated in plague infested buildings 

 where rats had been known to die of the disease. Within several hours 

 they had collected scores of rat fleas, and in turn became infected with 

 the plague. As many as 988 fleas were caught off* one guinea-pig. All 

 investigators, however, have not recorded similar successes with these 

 living traps. Some unknown factor, such as weather or temperature, 

 seems to affect the appetite of the fleas or their capacity or inclination 

 to wander about and find a new host in this manner, and sometimes the 

 guinea-pig did not collect a single specimen. 



The females of several species of fleas are sedentary and after finding 

 a suitable host, they collect on its head, either on the ears or in the 



