342 



THE MITES 



Itch Mites 



The itch mites, belonging to the family Sarcoptida?, are the 

 cause of scabies or mange in various kinds of domestic and wild 

 animals, and of " itch " in man. This disease is one which has 

 been known for a very long time but was formerly supposed to be 

 caused by " bad blood " or other constitutional disorders such 

 as cause the growth of pimples. Even at the present time the 

 true cause of the disease is not understood by the majority of 

 people. 



The Parasites. — The itch mites (Fig. 142) are minute whitish 

 creatures, scarcely visible to the naked eye, of which the females 



Fig. 142. Human itch mite, Sarcoptcs scahici; 9. female; $. malo. X about 



100. (Partly after Banks.) 



l)urrow beneath the skin and lay eggs in the galleries which they 

 make. They arc nearly round and the cuticle is delicateh' 

 sculptured with numerous wavy parallel lines, pierced here and 

 there by stiff projecting bristles or hairs. There are no eyes 

 or trache£e. The cone-shaped mouthparts are covered over l)y 

 the shicldlike upper lip. The legs are short and stumpy and are 

 provided with sucker-like organs, called ambulacra, at their 

 tips. In the female the two posterior pairs of legs terminate 

 in a simple long bristle, whereas in the male only the third pair 

 of legs terminates in bristles. The human itch mite, Sorcoptcs 

 scahiei, is only .slightly distinguishable from the itch mites which 

 cause scabies and mange in many of our domesticated animals. 

 Each infected species of mammal has its own variety of itch 



