166 LIFE HISTORY OF NORTH AMERICAN TICKS. 
long (from tip of palpi to base of emargination of scutum); scutum 
0.241 mm. long by 0.350 mm. wide. 
Egg.—The average size of 10 eggs measured was 0.645 by 0.460 
mm.; light brown, shining, smooth. 
HOST RELATIONSHIP. 
The host of the type of this species is not known. Most of the infor- 
mation herein presented regarding the host relationship of the species 
was obtained in the Bitter Root Valley of Montana. The work 
there was conducted under the general supervision of Mr. W. D. 
Hunter, but under the immediate direction of Prof. R. A. Cooley. 
Mr. W. V. King, of the Bureau of Entomology, and Mr. C. Birdseye, 
of the Bureau of Biological Survey, spent the spring and summer, 
and Mr. A. H. Howell, of the Biological Survey, a portion of the 
spring of 1910 in the center of the area where Rocky Mountain spotted 
fever occurs in its most virulent form. Messrs. King and Birdseye 
continued this investigation throughout 1911 in the same locality. 
To these men, who exposed themselves to the dangers of infection in 
order to collect information regarding this tick and its hosts, we are 
greatly indebted. In order to identify with certainty the species of 
ticks collected, the immature stages were sent to the laboratory at 
Dallas, Tex., and reared to adult and determined. It has been found 
that practically all of the small mammals act as hosts for the larvee 
and nymphs, while the adult stages are seldom found on other than 
the large domestic animals. Horses and cattle appear to be by far 
the preferred hosts. Among other domestic animals upon which 
adults have been found are sheep, mule, ass, dog, hog, goat, and cat 
(probably unattached). The principal wild mammals found to act 
as hosts for this stage are the mountain goat, brown bear, coyote, 
woodchuck, rabbit, wild cat, and badger. .The last three appear to 
be rarely attacked by the adults of this species. The immature stages 
have been taken on the following hosts which are arranged approxi- 
mately according to their relative importance: Ground squirrel ( Citel- 
lus columbianus), pine squirrel (Sciurus hudsonicus richardsont) , chip- 
munks (Futamias lutewentris, Eutamias quadrivittatus umbrinus), 
rock squirrel (Callospermophilus lateralis cinerascens), woodchuck 
( Marmota flaviventer), rabbits (Sylvilagus nuttalla and Lepus bairdi), 
wood rat ( Neotoma cinerea), gray meadow mouse ( Mcrotus nanus 
canescens), pika (Ochotona princeps), white-footed mouse (Peromyscus 
maniculatus artemisiz), large meadow mouse (Microtus modestus), 
jumping mouse (Zapus princeps), and pocket gopher (Thomomys 
fuscus). 
Dr. H. T. Ricketts and Prof. R. A. Cooley have given a consider- 
able amount of information on the host relationship of this species. 
Dr. Ricketts states that in Idaho this tick was found on the snow- 
shoe rabbit (Lepus bairdi) in considerable numbers in all stages of 
