CHAPTER XXI 

 TICKS 



While mites as a group are extremely annoying pests, with one 

 exception they are not dangerous as disease carriers. The ticks, 

 on the other hand, are not only annoying but dangerous. Several 

 important diseases of domestic animals are transmitted solely by 

 ticks, and several human diseases are likewise dependent on 

 ticks for dissemination, especially African relapsing fever or 

 " tick fever " and Rocky Mountain spotted fever. In addition 

 to this, tick bites, at least those of some species, give rise to a 

 serious form of paralysis, especially in children, which may end 

 in death. Tick bites also frequently give rise to dangerous 

 ulcerating sores which may result in fatal blood poisoning. The 

 economic importance of ticks as parasites of domestic animals is 

 not for consideration here, but it would not be amiss to state 

 that the annual loss in the United States from cattle ticks alone 

 is estimated at from $40,000,000 to $50,000,000. It is evident 

 that ticks should be looked upon as worthy candidates for ex- 

 termination wherever this is possible. 



Although the ticks constitute only one of several divisions of 

 the order Acarina, they are so readily distinguishable and so 

 weU known that in the popular mind the ticks are looked upon as 

 a group quite distinct from all other mites, and equivalent with 

 them. They are of relatively large size and usually exceed all 

 other Acarina in this respect even in their larval stages. Some 

 species when full grown and engorged are fully half an inch in 

 length. 



General Anatomy. — The body of a tick is covered by a 

 leathery cuticle which is capable of great expansion in the fe- 

 males as they engorge themselves on their host's blood, filling the 

 numerous complex pouches of the digestive tract (Fig. 149). 

 When not engorged ticks are flat and oval or triangular in shape 

 (Fig. 154), usually tapering to the anterior end, but after en- 

 gorgement they resemble beans or nuts of some kind (Fig. 158). 



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