340 OUR HOUSEHOLD INSECTS 



probably the most disgusting and hated of all the para- 

 sites to which mankind is subject. The thorax is much 

 broader than in the other two species, and is even wider 

 than the abdomen itself. This great and sudden width 

 of the thorax, combined with the shortness of the abdo- 

 men and the lateral expansion of the legs, give it a 

 crab-like shape, which is the origin of its popular name. 

 The two hind pair of legs are much stouter than the 

 front pair, and their claws are very strong, and curved 

 completely back upon the foot, giving it an intense 



FIG. 113. Crab Louse (Phthirius inguinalis). 



clinging power. It ranges from ^ to T ^ inch in length, 

 and its life-history is similar to that of the rest, though 

 it appears to multiply rather more rapidly, and to be 

 communicated rather more freely. As its scientific 

 name implies, it is an inhabitant chiefly of the groin, 

 though when it exists in swarms, as is sometimes the 

 case, it may be found on other parts of the body as well, 

 such as the breast, the arm-pits, the beard, the eyebrows, 

 and even the eyelashes. A frightful degree of multipli- 

 cation of this insect, or of P. vestimenti, is either the 



