April, ’18] 
PARKER: ROCKY MOUNTAIN SPOTTED FEVER TICK 
191 
the horses would undoubtedly show the higher average. Jack rabbits 
are especially efficient as nymphal hosts, the latter engorging in much 
less time than on any other animal and may be present in large num¬ 
bers. Cottontail rabbits are also important, but principally as hosts 
of the immature stages; and it is likely that they are susceptible to the 
disease. 
Interesting observations of the past two seasons have pointed to a 
frequent coincidence of the abundance of ticks and the abundance of 
jack rabbits preceding the occurrence of cases of the fever. It is well 
known that in many regions rabbits will suddenly increase greatly 
after several years of relative scarcity and then after a few years of 
abundance will as suddenly die off, due to causes not well understood. 
The intervals between the epidemics are variable but seven years has 
frequently been recorded, though it may be more or less. At Powder - 
ville rabbits reached their maximum abundance in 1914 and died off 
in great numbers during the winter of 1914 to 1915 and for some time 
thereafter. The latter year was that of great tick abundance and also 
that in which several cases of fever occurred in that region. It is not 
desired to direct attention to the possible influence of rabbits on the 
periodical abundance of ticks, however important that may be, but 
rather to point out that a periodic increase in rabbits means a peri¬ 
odic increase in an animal highly susceptible to spotted fever, and 
when it so happens that an increase in ticks is coincident, it is reason¬ 
able to suppose that if infection is present in nature, then a consid¬ 
erable increase in the number of infected ticks becomes possible. The 
occurrence of fever following a parallel increase in rabbits and ticks, 
therefore becomes of interest. The data indicate the possible control 
of spotted fever under eastern Montana prairie conditions by the 
eradication of rabbits: conclusive evidence will be sought in our future 
field operations. 
Porcupines .—Several of these animals examined under prairie con¬ 
ditions late in the season of 1916 were infested with adult ticks, one 
a fully engorged female. The likelihood that they might be impor¬ 
tant adult hosts has since been strengthened by emphatic statements 
by ranchers and further observations. More than 20 adult ticks have 
been found on a single animal and a seasonal average of 6.8 was ob¬ 
tained in 1917. Where numerous these animals are surely of some 
importance. 
Deer Mice .—Next to the jack rabbit, the deer mouse is certainly the 
most important wild mammal in eastern Montana, considered as a 
whole, in relation to the tick. The reasons for this are,—first, it far 
exceeds in abundance all other wild mammal hosts of immature ticks 
combined, second, its wide distribution and its adaptability to all 
