SEASONAL HISTORY AND HABITS. 25 
their winter quarters for some time, the last individuals not securing 
hosts upon which to engorge until early in July. These individuals 
molt to adults during the latter part of the summer, and the resulting 
adults pass the winter before feeding. 
In contrast to the short length of life as exhibited by the larva, 
we find the vitality of the nymphs and adults to be remarkably 
great. It has been determined that adults collected on vegetation 
during the spring months may survive for a period of 413 days 
without food. These individuals undoubtedly passed the winter in 
the adult stage, and therefore the total length of life must have been 
approximately one and two-thirds years. However, in nature the 
great majority of the ticks with a vitality equal to this lot would 
probably find hosts and become engorged. Unfed nymphs have been 
found to survive a period of more than 300 days. It is thus possible 
for ticks which pass the winter in the nymphal stage to live until 
at least July 15 of the following year. Under natural conditions 
this longevity is probably even greater. 
The following is a summary of the life cycle of the tick: The 
winter is passed as flat or unengorged males and females and as un- 
engorged nymphs. The former are present from about March 15 
to July 15, during which time they find hosts and become engorged. 
It is during this period that the pest attacks man and communicates 
to him the germs of Rocky Mountain spotted fever. The eggs de- 
posited by the females which find hosts early in the spring hatch 
into larve, which may develop into adults by the first or middle of 
September. The offspring of the females which become engorged late 
in the season succeed in developing only as far as the unengorged 
nymphal stage before cold weather begins. The overwintered 
nymphs begin appearing from their winter quarters during the latter 
part of March. They are to be found upon small wild mammals from 
that time until about the middle of July, at which time the nymphs 
which have developed from the females engorged during that spring 
are also present. Overwintered nymphs transform to adults during 
the summer and fall, and the majority of these adults pass the 
winter in the unfed condition. A few of the first nymphs to find 
hosts early in the spring may molt to adults sufficiently early in the 
summer to allow the adults to become engorged, deposit eggs, and 
the transformation to proceed to the unfed nymphal stage by the 
appreach of cold weather, thus completing a life cycle in one year. 
However, the individuals which proceed with development beyond 
the unengorged adult stage during the same season must be very 
exceptional. When the mean temperature is low during the spring 
and early summer it is almost certain that none of, the individuals 
which have passed the winter as unengorged nymphs develop further 
than unengorged adults during that season. 
