ECONOMIC IMPORTANCE, 19 
Within 3 days 14 pounds, by weight, of ticks which had dropped from 
this horse were collected, and this amount represented only about 
one-half of the total number of ticks which engorged upon it. After 
dropping, their places of attachment furnish points at which the 
screw-worm fly (Chrysomyia macellaria) deposits its eggs, the mag- 
gots from which then readily enter the host. In the Southwestern 
States the appearance of equines is frequently injured by screw- 
worms, which gain entrance at the points in the ears where ticks 
had been attached, burrow, and destroy the supporting cartilage, 
causing the ears to lop over. This condition is commonly known as 
‘‘gotched.”’ Not the least of all is the frequent annoyance which 
man suffers as the result of the attachment of ticks to his body. 
The ticks which molt upon the host, instead of having to wait long 
periods to find another, merely continue sucking blood from the 
same animal. As a result these ticks reproduce very rapidly and 
frequently become of much greater importance as external parasites 
than species which drop to molt. This is the case with the cattle tick. 
Those which drop to molt have overcome this great disadvantage by 
becoming more resistant to heat and cold and by having gained the 
power to withstand much longer periods of fasting. Certain members 
of the subfamily Ixodine, while not occurring in such great numbers 
on animals as in the case of species which molt on their hosts—all of 
which belong to the subfamily Rhipicephaline—are frequently of 
considerable importance as pests, owing to the fact that the great 
length of the hypostome permits deep penetration. As the result of 
this deep penetration by the [xodine, an inflammation is produced 
which frequently results in suppuration. Often in the attempt to 
remove ticks belonging to this latter class from the body of the host, 
the capitulum is separated from the body of the tick and remains 
embedded in the host. 
The periods in the life history of ticks of particular importance 
economically and which should be determined are: Longevity, or the 
period required forstarvation while awaiting a host; minimum parasitic 
period, which is used in connection with the preoviposition and incu- 
bation periods to determine the time that tick-free areas may be used 
after infested cattle are turned in before the areas become infested; 
maximum parasitic pervod, or the period required for cleaning the host 
of all ticks (except males) when kept in tick-free inclosures; preovi- 
position period and minimum incubation period, used with the mini- 
mum parasitic period to determine the time that tick-free lots may be 
used before becoming infested; stage or stages of imbibition of infec- 
tion and the stage or stages in which infection is transmitted, i. e., in 
the case of species involved in disease transmission. 
