390 



LICE 



of these two' species. The females, which are somewhat larger 

 than the males, reach a length of about one-eighth of an inch. 

 Due to their dirty white or grayish color these lice are familiarly 

 known as " gray-backs." This species is known to be instru- 

 mental in transmitting both 

 typhus fever and European 

 relapsing fever. 



As the name "body louse" 

 implies, this species inhabits 

 the trunk rather than the 

 head. The German name 

 " Kleiderlaus ", meaning 

 " clothes louse ", is still better, 

 since this louse has so far 

 adapted itself to its host as 

 to have broken away from 

 the custom, prevalent among 

 all other species of lice, of 

 living in the hair of the body, 

 and to have established the 

 habit of living on the cloth- 

 ing. Just when, in the proc- 

 ess of our evolution from a 

 hairy ancestor, this louse 

 shifted its position from the 

 waning hair to the more and more habitually worn clothes would 

 be interesting to know. Not unlikely both this louse and the 

 closely allied head louse have evolved from a species which once 

 roamed the hairy bodies of our forefathers, each species coping 

 with the unfavorable circumstance of the developing hairless- 

 ness of its host in a different way, the more conservative head 

 louse withdrawing to the fine hair of the head, the body louse 

 adapting itself to living on the clothing. 



A person infested with thousands of body lice may remove his 

 clothing and find not a single specimen on his body. An exami- 

 nation of the underwear will reveal them adhering by their long 

 claws to the surfaces which were next to the body. Here they 

 live and lay their eggs, leaving the clothing only long enough to 

 suck a meal of blood, even then usually adhering to the clothes 

 by their hind legs. 



FIG. 174. Body louse, Pediculus humanus, 

 male; ant., antenna; e., eye; p., penis; sp., 

 spiracles; th., thorax. X 25. 



