February, '15] 



COOLEY: SPOTTED FEVER TICK 



49 



under laboratory conditions and he collected ticks in nature and dem- 

 onstrated their infectivity by allowing them to bite guinea pigs in 

 which he had previously learned to diagnose the disease with certainty. 



As bearing further evidence, it may be stated that the only pre- 

 caution which the entomologists have taken in the work in the valley 

 has been against being bitten by ticks and though living in even more 

 apparent danger than the residents themselves, none has been infected. 



Geographical Distribution of the Tick 



The spotted fever tick occurs in the following states \' Washington, 

 Oregon, Idaho, Montana, Wyoming, Nevada, Utah, Colorado, Cali- 

 fornia and New Mexico. It also extends northward into British Colum- 

 bia. 



Only a small proportion of the ticks in the Bitter Root valley are 

 infective and throughout the geographical range of the species, only 

 here and there a locality occurs which contains any infective indi- 

 viduals. 



Life-History 



An intimate understanding of the life-history of this tick comes only 

 through a knowledge of the host relationships in the various stages, 

 the habits and abundance of the host animals, and the relation of the 

 development of the tick to the succession of seasons. 



These subjects will be briefly reviewed. 



Host Relationships. — The larvae and nymphs use very much the 

 same list of mammals as hosts, and availability is apparently a greater 

 factor than choice in determining what species of mammals shall be 

 used. Practically all the species of small mammals occurring in the val- 

 ley have been found to serve as hosts, but the ground squirrel (Citellus 

 columbianus) , the pine-squirrel {Sciurus hudsonicus richardsoni) and the 

 chipmunk {Eutamias luteiventris) , because of their numbers and activ- 

 it}^, undoubtedly feed the great bulk of all the larvae and nymphs that 

 secure food. The adults feed only, or with few exceptions, on large ani- 

 mals. Under the conditions that prevail in the Bitter Root valley, as 

 distinguished from the contiguous mountains, practically all of the 

 adults that are fed use domestic animals, horses and cows princi- 

 pally, as hosts. Back into the mountains, ticks become less abundant, 

 disappearing almost entirely when the limit of the range of domestic 

 animals is reached. 



Still further back, beyond this limit, in the ^'goat country," as it 

 is called, or the natural habitat of the Rocky Mountain Goat {Oream- 



1 Bishopp. Distribution of the Rocky Mountain spotted fever tick. Circular 136, 

 Bureau of Entomology, 1911. 



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