204 



Nature-Study Agriculture 



External 

 parasites 



The 



Texas-fever 



lick 



W. T. Shilling 

 FiG. 158. A parasitic insect laid its eggs 

 within the body of this caterpillar. When 

 the eggs hatched, the grubs bored their 

 ,way through the skin of the caterpillar 

 and formed pupae. 



Insect parasites on the 

 larger animals. There 

 are many parasites that 

 infest larger animals in- 

 stead of living upon 

 other insects. Some of 

 these live within the 

 host, but others stay on 

 the skin and suck the 

 blood of the host. Ex- 

 amples of the latter are 

 the tick, the flea, the 

 louse, and the mosquito. 



External parasites are 

 not only very annoying 

 to animals, but some of 

 them do an immense 

 amount of damage. The 

 Texas-fever tick, found 

 upon cattle in Mexico 

 and along the southern 

 border of the United 

 States, causes a fever 

 from which many cattle 



die. To free the cattle from it, they are dipped in a 

 poisonous solution contained in a large tank through 

 which the cattle are driven (Fig. 159). To prevent 

 Mexican cattle from bringing the insect across the 

 line into California, our government has built a 

 barbed-wire fence along the border between the 

 two countries, beginning at the Pacific Ocean and 



