180 LIFE HISTORY OF NORTH AMERICAN TICKS, 
the large mammals between March 10 and June 10, then engorge 
and deposit eggs from which larve hatch. These larve engorge 
upon small mammals and drop and molt to nymphs which, in some 
cases, May remain quiet until cool weather begins and then go into 
hibernation to appear as unengorged nymphs the following spring. 
Others probably become engorged and in the fall produce adults 
which pass the winter in that stage. The over-wintered nymphs 
appear somewhat later than the adults; they attach to small mam- 
mals, become engorged, and produce adults. The majority of these 
adults probably remain quiet during the summer and go into hiber- 
nation the following winter. 
ECONOMIC IMPORTANCE. 
While this species appears to be quite abundant in certain portions 
of the northwestern United States and more or less annoying to 
domesticated and wild animals, it is of particular importance because 
of the réle it plays in the transmission of the causative organism of 
Rocky Mountain spotted fever. This is a disease of man which occurs 
in several of the Rocky Mountain States. It is of extreme importance 
in the Bitter Root Valley of Montana, where a number of cases occur 
each year, among which the mortality is usually about 70 per cent. 
In Idaho, however, the disease is much less virulent, the mortality 
not running above 5 to 8 per cent, although the number of cases in 
the southern part of this State frequently exceeds 300 per year. 
The occurrence of the disease is largely eonfined to the spring 
months March to June inclusive, or the period during which the 
adult ticks are most active. 
NATURAL CONTROL, 
Few observations relating to the natural enemies of this species 
appear to have been made. Chickens have been found to devour the 
engorged females with avidity when the ticks were fed to them. No 
doubt fowls eat a large number of ticks which drop from animals 
in the barnyard. In Colorado a species of blackbird was seen to 
devour the engorged ticks as they fell from cattle. Engorged females 
have been observed to be eaten by tame rabbits upon which speci- 
mens were being engorged. The little black ant, Monomorium 
minumum, was found on a number of occasions to have entered pill 
boxes which contained engorged larve and destroyed dozens of 
specimens. 
ARTIFICIAL CONTROL. 
As has been pointed out, the adults of the Rocky Mountain spotted- 
fever tick feed almost exclusively on the large domestic animals, 
while the small rodents are the principal hosts of the immature stages. 
This immediately suggests the idea of destroying the adult ticks on 
domestic animals, On account of the fact that many of the adults 
