242 



PARASITIC DISEASES 



than tick, as its entire life is spent on the body of a sheep. The 

 general color of the body is brown. The legs are stout, covered 

 with hair and armed with hooks at their extremities. The mouth 

 parts consist of a tubular, toothed proboscis with which the para- 

 site punctures the skin and sucks the blood. Within a few hours 

 after birth, the larvae develop into pupip, which are hard, dark 

 bro'wn in color and firmly glued to the wool. The young louse- 

 fly emerges from the pupa in 

 from three to four weeks. 



The sheep-tick is a very 

 common external parasite. 

 The adult parasites and the 

 pupaj are large and easily 

 found. When badly infested 

 with ticks, a sheep will rub, 

 dig and scratch the skin and 

 fleece. This results in pieces 

 of wool becoming pulled out 

 and the fleece appears ragged. 

 After clipping the ticks mi- 

 grate from the ewes to the 

 lambs, which may become un- 

 thrifty and weak. 



The treatment consists iti 

 dipping the flock in a one or 

 two per cent water solution of a coal-tar dip. Dips containing 

 arsenic are most effective in ridding sheep of ticks. 



Scabies. — This parasitic disease is one of the oldest and 

 most prevalent diseases of the skin. It is commonly known as 

 scab or mange. The animals most commonly affected are sheep, 

 horses and cattle. 



The disease is caused by small mites or acari that are natu- 

 rally divided into the t<arcoptes, which burrow under the epi- 

 dermis, forming galleries ; the Psoroptes, which live on the sup 



Fig. 67. — Sheep scab mite, ventral view. 

 (From Farmers' Bulletin No. 159, United 

 States Department of Agriculture.) 



