310 



HOUSEHOLD INSECTS 



body. It occurs, chiefly, on individuals of uncleanly habits 

 and especially on children who may become infested from 

 contact with their playmates at school or other places 

 (Fig. 106). 



The constant movements of the lice and the insertions of 

 their beaks into the skin to suck blood set up an irritation 

 which the victim tries to allay by scratching. Railliet 

 says the irritation leads to the production of papules or 

 even to vesicular pustules and 

 that the excoriations due to 

 the scratching with the exuda- 

 tions therefrom often form a 

 crust that mats the hairs to- 

 gether. Such a condition 

 exists only among very un- 

 clean people where the para- 

 sites are allowed to increase 

 indefinitely. 



The sexes of this louse differ 

 quite markedly from each 

 other. The female is about 

 one-twelfth of an inch in 



length and usually larger than the male, sometimes twice 

 as large. They multiply rapidly, for the female is capable 

 of laying (Railliet) at least fifty eggs in the space of six 

 days and each egg will hatch in about six days, while the 

 young lice may become adults in about eighteen days. 

 Thus there may be, under the most favorable conditions, 

 a complete generation within one month. At this rate 

 the second generation would number 2500 individuals, 

 while the third generation would furnish 125,000 of these 

 obnoxious pests. Fortunately, such conditions probably 



FIG. 106. Head louse. 

 (X 13.) 



