THE SPIDERS AND ALLIES 



143 



an organism which produces a very serious human disease 

 called Rocky Mountain spotted fever. In the Bitterroot 

 valley of Montana more than 75 per cent of the cases end 

 in death. Texas fever, a disease of cattle in the southern 

 part of the United States, is due to a parasite also carried 

 by the bite of a tick (Margar'opus annula'tus, Fig. 80). 

 The disease carried by this tick has resulted in cattle losses 

 in the Southern states amounting to millions of dollars. 



Fig. 81. Itch mites burrowing in the skin of man. (Enlarged) 



Mites as Parasites. There are many species of these mi- 

 nute, almost microscopic animals. Some of them are para- 

 sites of man. The harvest mites, or chiggers, are common in 

 woodland pastures in midsummer. Young harvest mites 

 have the habit of burrowing into the skin of man, where 

 they set up intense irritation and severe itching. The pecul- 

 iar part of it is that these mites which attack man commit 

 suicide by doing so. Only the ones which become attached 

 as parasites on the bodies of insects reach maturity. The 

 itch mites (Fig. 81) are another type of almost microscopic 

 creatures which burrow beneath the skin and lay their eggs 

 in these burrows. One species (Sarcop'tes scab'iei) produces 



1 Reprinted by permission from Ha ndbook of Medical Entomology, by W. A. Riley 

 and 0. A. Johannsen, published by The Comstock Publishing Co. 



