April, ’18] - PARKER: ROCKY MOUNTAIN SPOTTED FEVER TICK 
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these animals in the order given, the per cent of females showing en¬ 
gorgement was 74.42, 60.93 and 24.61; the per cent over .5 engorged 
was 3.86, 1.75 and 0 (average per animal .29, .11, .00); and the per 
cent over .8 engorged was 2.70, 1.46 and 0 (average per animal .29, 
.20 and 0). No females more than .2 engorged were found on pigs. 
It is of interest to compare some of the facts given above with those 
which govern the control system used in the Bitter Root Valley. Con¬ 
trol there is dependent on the facts that adult ticks are essentially 
confined to domestic animals and that the Columbian ground squirrel 
is by far the most important small mammal as host of larval and nym- 
phal ticks. In eastern Montana, on the other hand, the adults are 
not confined to domestic animals but the jack rabbit is also an exceed¬ 
ingly important host, with the porcupine as an able accessory. Also 
instead of one small and easily controlled mammal as the most impor¬ 
tant host of the young ticks, we find several efficient hosts, their rela¬ 
tive importance frequently depending on local conditions. Mice, 
seemingly of scant importance in the Bitter Root, are one of the im¬ 
portant problems in the east. 
Relationjof the Character of the Country to the Abundance 
of Host Animals and of Ticks. —A thorough comprehension of the 
tick problem in eastern Montana, and probably in many other places 
where the milder type of the fever occurs, involves an accurate knowl¬ 
edge of the effect which the character of the ground and the floral 
setting has on the abundance of the tick, and the reasons therefor. 
Other factors being favorable, the abundance of ticks depends to a 
large extent on the character of the ground, whether rocky or clear, 
and upon the nature of the vegetation. It is these factors which deter¬ 
mine the species of host animals and their relative abundance. For 
example, in a prairie country, only prairie animals, of which the jack 
rabbit is one, can become really numerous, while species such as the 
chipmunk that are not adapted to such conditions can never become 
sufficiently numerous to be a real factor in tick abundance. Another 
example is furnished by the conditions existing in the hill country. 
There the ticks were found largely confined to the rocky slopes between 
the valleys and the hills and in the coulees. This was because it was 
in these places that the deer mice and chipmunks, previously men¬ 
tioned as the important hosts of that region, found the most favorable 
habitat conditions. Whenever ticks were numerous under other con¬ 
ditions it was explainable by the presence of other host animals adapted 
thereto. Mention has already been made of the fact that field mice 
were of importance only where conditions particularly favored them. 
It has also been found that certain animals which, under prairie con¬ 
ditions, are found both in rocky places and in rock free areas, always 
