=, 
LIFE HISTORY OF CATTLE TICK. 25 
ticks, but that such a temperature continued for 24 hours resulted in 
the death of practically all. Our experiments have been of two 
classes—(1) in water and (2) without water. In both cases the seed 
ticks were subjected to a temperature somewhat less than 32° F. In 
the case where water was supplied solid ice was obtained. Both in 
and out of water the seed ticks survived a freezing temperature of one 
hour’s duration, although there was perceptible mortality among 
them. 
LONGEVITY OF SEED TICKS. 
The time that seed ticks may survive without a host is a most 
important matter in plans for control. Our experiments on this 
point have been of two kinds—(1) with seed ticks from eggs deposited 
by females placed on the ground in favorable circumstances, thus 
giving absolutely natural conditions, and (2) with seed ticks in glass 
tubes, where they could be observed more closely. 
In the first series, which was instituted at the suggestion of Pro- 
fessor Morgan, several hundred engorged ticks were placed on the 
ground at regular intervals. The only inclosure was a cylinder of 
2-inch-mesh wire screen about 4 feet in diameter to prevent disturb- 
ance. The seed ticks from females placed under these conditions 
.accumulated in enormous numbers on the blades of grass or stakes 
provided for the purpose (see Pl. I, fig. 2). Table V gives the num- 
ber of days the seed ticks survived in these experiments, together 
with other data. It will be seen that the shortest period was 49 
days and the longest 159+ days. However, the important period 
is from the time of dropping of the adults to the death of the resulting 
seed ticks, since the farmer must always suppose in rotating his cat- 
tle that adults were dropped on the day of removal from the pasture 
which it is desired to clean. This period ranged from 91 to 175+ 
days. It will be noted that there is considerable variation in the 
period of survival, even at the same season of the year. This seems 
to depend upon two factors, namely, the number of seed ticks in the 
bunches and the amount of rainfall. The larger masses survive 
longer, perhaps because the moisture is better retained, and heavy 
rains scatter and reduce the masses. It is probable, on account of 
the very large numbers of seed ticks in our experiments, that the 
periods given in the tables are somewhat longer than normally occur 
in the field. However, such excessive numbers do sometimes occur 
in nature. For instance, when an animal dies of gross infestation 
thousands of ticks deposit in a very restricted area. Mr. J. D. 
Mitchell has seen cases of this kind in which the bunches of seed ticks 
were fully as numerous as in our experiments. 
