408 FLEAS 



The exact identification of fleas, especially if the host is un- 

 known, is difficult, being based largely on such minute charac- 

 teristics as relative lengths of different segments of the legs, 

 number and distribution of spines, etc. Most species of fleas, 

 however, are quite closely confined to their respective hosts, only 

 a few species being able to thrive on a number of different hosts. 

 Some of the commoner species of the fleas which are of most im- 

 portance to man can be fairly closely identified, if the host and 

 geographic locality is known, by the presence or absence of the 

 " combs " on the head and thorax. The common human flea, 

 Pulex irritans (Fig. 179 A), and the Indian rat flea, Xenopsylla 

 cheopis (Fig. 177), have no combs, the common rat and squirrel 

 fleas of temperate climates (Figs. 179C and 178) have only the 

 thoracic comb, while the cat and dog fleas (Fig. 179B) have both 

 facial and thoracic combs. 



Life History and Habits. — The life history of all fleas is 

 quite similar. Like the Diptera, or flies, they pass through a 



complete metamorphosis, 

 i.e., undergo a complete 

 reorganization from larval 

 to adult form during a 

 resting pupal stage. The 



Fig. 180. Larva of Indian rat flea, Xenop- eggS are OVal, whitish in 

 sylla cheopis. X 12. (After Bacot and Ride- , j i .■ i i 



Joqj ) color and relatively large, 



often one-third the length 

 of the parent flea, and are laid singly, except in the chiggers, 

 being dropped at random in the fur of the host or in the lairs or 

 habitations of the hosts. The human flea, for instance, lays its 

 eggs in the dust and debris in cracks in floors, under carpets, 

 etc., whereas the fleas of most mammals lay their eggs loosely in 

 the fur of the host, whence they drop off when the animal shakes 

 himself or prepares to sleep. The time required for the eggs to 

 reach the hatching stage varies with the species and with climatic 

 conditions from two or three days to over two weeks. 



The larvae (Fig. 180) are tiny cylindrical maggot-like creatures 

 with neither legs nor eyes. They have small brown heads and 

 whitish bodies composed of 13 segments, which are provided with 

 rather sparse bristly hairs to aid in crawling. The last segment 

 is terminated by a pair of tiny hooks. 



The larvse squirm about actively in the dirt or debris of the 



