96 LIFE HISTORY OF NORTH AMERICAN TICKS, 
for 342 days. They may engorge in 4 days after attachment and 
begin molting 13 days after dropping. A total effective temperature 
of about 486° F. is required to produce this transformation. Adults 
may live for 588 days without food. Both sexes have been found 
together in abundance on wild hosts, but copulation has not been 
observed in ticks reared experimentally. Females may drop engorged 
in 17 days after attachment to a host. 
The three stages of the rabbit tick have been taken from hosts in 
nature during all seasons of the year. We have found the immature 
ticks in great numbers on ground-inhabiting species of birds in the 
fall and winter; they may, however, be equally numerous in the 
summer. 
ECONOMIC IMPORTANCE. 
On account of the fact that this tick confines its attack to rabbits 
and wild birds, it is of no importance economically. In a few 
instances the species has been known to become so abundant on wild 
rabbits as to render them so weak that they could be easily killed by 
their enemies. Mr. W. V. King killed two snowshoe rabbits (Lepus 
bairdi) at Florence, Mont., on April 3, 1910, which were infested 
with 1,033 ticks. Many of these were fully engorged females. The 
large number of specimens found on quail and meadowlarks leads us 
to believe that in some cases the young of these hosts may be killed 
by tick attack. 
NATURAL CONTROL. 
The bird hosts of the rabbit tick undoubtedly destroy a considerable 
number of them, although they also serve as disseminators of the 
species. As has been stated, rabbits have been observed by us to 
devour engorged ticks and no doubt some specimens are injured by 
the scratching of this host. The smaller birds, such as sparrows, 
and certain reptiles and batrachians, are also probably of some 
importance in the destruction of this tick. It is known that this 
species 1s parasitized in the nymphal stage by a chalcidid. This 
parasite (Ivodiphagus texanus), the first recorded as having been 
reared from a tick, was described by Dr. L. O. Howard (1908) from 
individuals reared at the tick laboratory from engorged nymphs 
collected by Mr. J. D. Mitchell in Jackson County, Tex. A single 
specimen in each of two different lots of engorged nymphs was found 
to be parasitized by this insect. One of these lots was collected 
March 10, 1907, on a cottontail rabbit and the other May 1, 1907, ona 
jack rabbit. Subsequent collections in that locality have failed to 
reveal other parasitized specimens. 
