204 



SCHOOL KNTOMOLO<;Y 



animal is not treated. The innumerable little mites sucking 

 from the skin cause an intense irritation and a consequent 

 secretion of a large amount of serum. This forms at first a 

 dandruff and later a thick scab. As this goes on the wool 

 drops off, the sheep loses flesh, and presents a very unkempt 

 appearance. If badly infected and untreated, sheep may 

 be killed by the injury. The only sure diagnosis of the 



FIG. 145. The sheep scab mite (Psoroptes ovis). (After Good, Ky. 

 Agr. Exp. Sta.) 



a, female; b, male both very greatly enlarged. 



scab is to find the mites. This can be done by placing some 

 of the suspected scabby material on a black background in 

 a warm place, when the small mites may be detected crawl- 

 ing around, the more readily by the aid of a magnifier. The 

 scab mites are spread from one animal to another by con- 

 tact and by the sheep coming in contact with sides of cars, 

 fences, or other objects against which scabby sheep have 



