54 PRACTICAL ZOOLOGY 



readily through wool and sucks the blood from its host. The 

 loss of blood and the irritation caused by ticks hinders the 

 proper development of sheep and when lambs are attacked death 

 often occurs. To destroy ticks, sheep should be dipped after 

 shearing in solutions containing kerosene, tobacco, tar, etc. 



Such practice not only kills the ticks 

 but it also destroys lice and scab 

 mites if these are present. 



Lice. A fourth group of degen- 

 erate parasitic insects is made up of 

 the sucking lice. These also are 

 wingless. They possess mouth parts 

 adapted for sucking blood from the 



FIG. 33. Sheep tick. En- poultry, cattle, sheep, and other 



larged and natural size (in small domestic animals which they para- 

 circle). (Photo by O Kane.) J 



sitize, and also from man. Some 



kinds of lice have biting mouth parts with which they feed on 

 pieces of feathers. The commonest bird louse is the chicken 

 louse (Fig. 34, A), a pale yellow insect about one twenty- 

 fifth of an inch long. The eggs or " nits " are fastened to 

 the feathers, and the young, which hatch ten days later, 

 begin at once to feed on the feathers. The irritation caused by 

 the sharp claws of the lice often causes the fowls to dust them- 

 selves in the road or a dust box provided for them, thus removing 

 the lice. A mixture of sulphur and lime will help to rid both the 

 poultry house and the poultry themselves of their parasites. 



Sucking lice occur on a great many domestic animals, and 

 some, like the ox louse and hog louse, are often very injurious. 

 Those best known are the three that sometimes infest human 

 beings, the head louse, crab louse, and body louse (Fig. 34, B, C, 

 and D). These lice are small, gray or yellowish in color, and 

 elongate oval in shape. They fasten their eggs or " nits " to 

 the hairs of the body and live among them. Lice are, of course, 

 present only on unclean persons, and may be removed easily. 

 They are sometimes very numerous on men crowded together 



