358 THE DOMESTIC SHEEP. 



Recent exact knowledge now goes to help us greatly in strug- 

 gling with this and all other parasites of our flocks, but the 

 evil is so widespread and virulent, and there are so many who 

 keep sheep who will not take the pains needed to exterminate 

 all the pests of the flock, that it is hopeless to expect full deliv- 

 erance from them. And the shepherd must still be watchful, ex- 

 pert, and industrious, to avert the risks as far as may be possible. 



These parasites are external or internal, the former are few 

 in number, but the latter abound, and the variety of them is as- 

 tounding to those who study the matter in its full bearings. 

 Of the external enemies of this class which trouble the flock by 

 far the worst are: 



THE SCAB MITE. 



These are insects of the family known as Acari, in which is 

 included the common itch mite, which infests mankind. It also 

 includes three species which affect sheep. These are known as 

 the Sarcoptes scabici, which infests the head of the sheep; Psorop- 



FIG. 27. Scabby Sheep Taken from Photograph. 



tes communis, which infests the body, and Chorioptes communis, 

 which affects the feet. The life history of these insects is similar 

 in each ppecies. They attack the skin and bite it, and these 

 wounds so made form scabs, under which the pests lay their 

 eggs. Each female produces an average of ten young, which ma- 

 ture in fifteen days, thus in the short season of three months 



