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28 THE ROCKY MOUNTAIN SPOTTED FEVER TICK. 
Among the domestic animals which act as hosts for the adult 
stage of the tick, horses and cattle are of prime importance. A 
number of collections indicates that sheep are frequently attacked, 
but with smaller numbers of ticks. Dogs have also been found to 
harbor this species, but in limited numbers only. Among nearly 
100 collections of ticks made on dogs in the territory in which this 
species occurs only 12 lots of this tick have been obtained. Only 2 
of these 12 lots contained females which were sufficiently engorged 
to deposit eggs. This indicates that the majority of the ticks are 
scratched off by the dogs before becoming fully filled with blood. 
Mules and asses have also been found infested with this species, and 
in two instances collections have been made upon hogs. It is not 
likely that the latter host is of much importance, particularly when 
the animals are kept confined in pens and thus not exposed to the 
ticks. 
Among the wild animals which act as hosts for the adults, the 
mountain goat harbors by far the greatest number. In addition to 
specimens of the adults, nymphs have also been found upon them. 
The brown bear and coyote have been found to be infested with 
considerable numbers of spotted-fever ticks, some of the specimens 
being sufficiently engorged to deposit eggs. The snowshoe rabbit 
and jack rabbit have occasionally been observed to be infested with 
limited numbers of adults, but on neither of these hosts have en- 
gorged specimens been captured. The woodchuck has also been 
found to act as a host for the adult stage. In only one instance, 
however, were specimens taken upon this host, although 51 of the 
animals were examined during the investigation. 
The Columbian ground squirrel is undoubtedly by far the most 
important host of the immature stages of this tick in the Bitter Root 
Valley. In other parts of the Western States, where this species 
of ground squirrel does not occur, related species have been found 
to act as hosts for both of the immature stages of this tick. In 
the Bitter Root Valley 65 per cent of the 311 Columbian ground 
squirrels examined were found to be infested with immature ticks 
of the genus Dermacentor. Owing to the fact that very large num- 
bers of the immature stages of ticks belonging to the genus Derma- 
centor collected in the Bitter Root Valley were reared to adult and 
all found to be the Rocky Mountain spotted-fever tick, we can 
say with practical certainty that this is the only species of this genus 
which occurs on the small mammals in that locality. Second in 
importance as a host of the immature stages of this tick in the Bitter 
Root Valley is the yellow-bellied chipmunk. Thirty-seven per cent 
of 131 of these mammals which were examined were found to be in- 
fested with seed ticks and nymphs. The pine squirrel is also of much 
importance, as 29 per cent of the 181 mammals examined were in- 
