INSECTS AFFECTING MAN AND ANIMALS 203 



Sheep should stay in the dip at least two minutes, so as to 

 get thoroughly wet, and the head should be ducked under. 

 Sheep introduced into the flock should be dipped so as to 

 prevent the introduction of ticks and other insect pests. 

 Spraying the pens or enclosures with zenoleum, cresol, or 

 any similar creosote preparation, or with kerosene emulsion, 

 will kill all wandering ticks and scab mites and is, therefore, 

 a good practice. 



124. The Sheep Scab Mite.* The little mites (35, 49) 

 which cause sheep scab are not true insects, but belong to 

 the same class as spiders and all true mites. However, they 

 are commonly considered among the insect parasites of sheep, 

 of which they are probably the most important. The mite 

 is so small as to be scarcely recognizable without a magnify- 

 ing glass, the females being about one-fortieth of an inch 

 long and the males about one-sixtieth or about the size 

 of this period (.). They are light gray in color and resemble 

 minute spiders in shape, and have four pairs of legs, to the 

 third pair of which are attached some long thread-like 

 appendages. A female lays from 10 to 20 eggs which hatch 

 in from four to ten days. A new generation appears about 

 every two weeks so that the pest increases with enormous 

 rapidity and a sheep will soon become badly infested. Sheep 

 are the only animals affected. 



The first symptom which will indicate the need of exam- 

 ination for scab mites, is the rubbing of the back, sides, or 

 tail of the sheep against some object, or its biting at these 

 parts, due to the itching caused by the mites. The infected 

 spot may at first be very small, so as almost to escape atten- 

 tion, consisting first of a yellowish, dandruff-like substance, 

 but if it is scratched the sheep will respond with a nibbling 

 motion of the mouth. Large patches are soon formed if the 



* Psoroptes communis Furst. Class Arachnida. See page 21. 



