338 



THE MITES 



until they have become fully developed males and females. Her 

 abdomen in consequence becomes enormously distended so that 

 the rest of the body appears as only a tiny appendage at one side 

 of it. A gravid female (Fig. 139) fully distended may reach a 

 diameter of 1.5 mm. (-jV of an inch) whereas normally she measures 

 only 0.2 mm. (j^s of an inch) in length. Under the most favorable 

 conditions only six days may elapse from the time the young 

 females emerge from the mother before they reproduce a brood of 



their own. The brood varies 

 in number from a few dozen 

 to over 200. 



Like many other beneficial 

 things, these predaceous little 

 mites may become a distinct 

 nuisance, and many serious 

 outbreaks of infestation of 

 human beings by them are on 

 record, especially among the 

 grain threshers of the central 

 portion of the United States 

 and among laborers who handle 

 stored grains and other dry 

 foods. In our Middle West 

 their attacks have often been 

 attributed to harvest mites. In 

 Italy the rash produced by 

 louse-mites is called " miller's itch." Several outbreaks have 

 occurred in the United States due to the use of new straw mat- 

 tresses. The transformation of all the grain-moth caterpillars 

 into moths leaves the mites with their normal food supply cut 

 oif , and they are then ready to feed upon any flesh to which they 

 may have access in an effort to prevent starving to death. 



The itching rash produced begins about 12 to 16 hours after 

 exposiu"e to the mites. At first they produce pale hivelike spots, 

 which later become red and inflamed, and itch unbearably. 

 Little blisters, the size of a pinhead or larger, appear at the sites 

 of the bites and these later develop into little pustules. Scratch- 

 ing results in the formation of scabs, and when these fall off 

 dark spots which are slow to fade are left on the skin. The 

 rash and itching normally disappear within a week unless fresh 



Fig. 139. Louse-mite, gravid female. 

 X about 75. (After Brucker from 

 Webster.) 



