174 LIFE HISTORY OF NORTH AMERICAN TICKS, 
was undoubtedly delayed by the approach of cold weather, but the 
first instance, as well as other similar cases of variation in molting 
periods, are difficult to explain. Cooley (1909, p. 101) found nymphs 
which dropped August 12 to commence molting in 42 days, while 
others required 47 days. Ricketts states (1908, p. 102) that the 
period required for molting varies from 1 to 3 months, according to 
the temperature. 
After dropping, the nymphs remain rather active for from 3 to 
several days or even weeks, depending upon temperature and state 
of engorgement. When it is cool the activity continues for a longer 
period than during hot weather and partial engorgement has the 
same effect. The nymphs usually become inactive gradually and 
within a few days after complete quiescence the area around the 
anterior end and the antero-lateral borders begins to become white. 
Dr. Ricketts has found the engorged nymphs to remain active in 
Montana during July and August for from 2 to 4 weeks, while if 
placed in a refrigerator they remained active for as long as 3 months. 
The sexes can often be distinguished several days before molting 
occurs by the appearance of the color pattern of the adult showing 
through the skin. In one case the female shields were easily seen 
6 days before molting took place. Some days prior to molting the 
surface of the body of the engorged nymphs frequently becomes 
dotted with small drops of a yellowish transparent fluid exudate. 
Molting is accomplished in the same manner as observed in other 
species of Dermacentor. The old skin first becomes free from the 
body at the anterior end, then splitting occurs on each side just 
above the third pair of legs. Later this splitting extends forward 
on each side to the lateral angles of the scutum, where the splitting 
follows the edges of the shield and the two fissures meet at the tip 
of the scutum. In many cases the force exerted by the tick causes ~ 
the splitting to extend back around the ventro-lateral margin so 
that the skin is broken in two. In other cases the lateral fissures 
extend backward along the dorso-lateral border to the second festoon 
grooves where they follow these grooves toward the venter, the 
dorsal end of the skin forming a hinge which allows the escape of 
the tick. 
The length of the molting period of nymphs which transform to 
males and of those which become females is about the same. 
