94 LIFE HISTORY OF NORTH AMERICAN TICKS. 
GENERAL LIFE HISTORY. 
Although ticks are able to survive long periods of fasting—some 
species much longer than others—development takes place only 
following a period of attachment during which the blood of some 
animal, either warm or cold blooded, must be taken into the body, 
i. e., they are obligatory parasites.. Several writers have considered 
the possibility that ticks may subsist in part upon vegetable matter. 
Prof. Lounsbury, however, who has conducted extensive studies of 
these arachnids, states (1905) that he has no doubt that they derive 
nutrition exclusively from living animals despite the protracted 
periods that they often have to wait for hosts. They do, never- 
theless, imbibe water from the rain or dew upon herbage or from the 
soil. One of the writers has observed ticks kept in tubes, on dry sand, 
to imbibe water from the moistened sand. Many untrained observers 
have reported that engorged ticks give birth to living young. Ricketts 
(1909a, p. 104) mentions this phenomenon as having been described to 
him concerning Dermacentor venustus by a number of residents of the 
Bitter Root Valley, Montana. While the origin of such erroneous 
statements can not be determined, one explanation to be offered is that 
of mistaking some of the Kermes for ticks. Thus Kermes galli- 
formis has been sent to one of the authors by an entomological 
collector who supposed it to be a tick. With the Kermes was a 
statement to the effect that it had been found dead with young 
swarming from it. 
DEVELOPMENT. 
All ticks pass through four distinct life stages: (1) The egg, (2) 
the larva or seed tick (6-legged stage), (3) the nymph or yearling 
tick (first 8-legged stage), and (4) the adult. Ali the ixodid and 
one (or more) of the argasid ticks engorge and molt but twice before 
arriving at the adult stage. Two species of Ornithodoros are re- 
ported to remain inactive in the larval stage and pass the first molt 
before engorging blood. Some of the argasids molt twice or three 
times during the nymphal stage, and at least one species continues 
molting after becoming adult. The larve of Ornithodoros talaje, 
which species is now being studied, engorge, then drop and molt twice 
before the next engorgement. The ixodid ticks engorge but once as 
adults, and die following the completion of oviposition, while most of 
the argasid ticks engorge a number of times as adults, oviposition 
following each engorgement. 
MOLTING. 
There is wide variation in the molting habits of ticks, even among 
species of the same genus. Most of the ticks, both argasid and 
ixodid, molt while away from the host, and the habit of molting 
