THE ROCKY MOUNTAIN SPOTTED-FEVER TICK. 165 
pleted in 20 days, a total effective temperature of 850° F. or more 
being required. - 
ECONOMIC IMPORTANCE. 
This variety of Dermacentor paruma pertus has not been taken on any 
other host than the rabbit; hence it is of no importance economically. 
NATURAL CONTROL. 
Rabbits kept in cages have been observed to scratch off and devour 
fully engorged females. It seems probable therefore that some of 
these ticks suffer the same fate in nature. 
To test the effect of heat upon eggs of this species, a bunch of 
freshly deposited eggs was placed on the ground in the sun from 3.55 
p.m.untilsunset. When the eggs were put out the atmospheric tem- 
perature was 110° F. and the soil surface temperature was 133° F. 
The eggs were somewhat shriveled when taken in and later they dried 
up completely. They showed no sign of embryonic development, 
while acheck lothatched in9days. There islittledoubt that heat and 
dryness are important in controlling the abundance of this species. 
One of two nymphs collected on a rabbit at Green Valley, Cal., on 
June 11,1909, was found to be parasitized by Hunterellus hookeri. 
This is the same species which acts as a parasite of the nymphs of 
Rhipicephalus sanguineus. 
THE ROCKY MOUNTAIN SPOTTED-FEVER TICK. 
Dermacentor venustus Banks. 
The common name of this species is taken from the fact that it is 
the transmitter of the disease of man known as Rocky Mountain 
spotted fever. 
DESCRIPTIVE. 
Adult (Pl. XIV, figs. 1, 3, 5-9) —Males from 2.1 by 1.5 mm. to 
6by3.7by14mm. Females, unengorged, from 3.1 by 1.8 mm. to 5.1 
by 3 mm.; engorged, from 13.8 by 10 by 6.4 mm. to 16.5 by 11.4 by 
6.9 mm. Male reddish brown; scutum with an extensive pattern of 
white lines; usually but little white on the middle posterior region; 
legs slightly lighter than scutum; joints tipped with white; female 
with scutum mostly covered with white; abdomen reddish brown; 
legs as in the male. 
Nymph. —Unengorged, from 1.36 by 0.72 mm. to 1.54 by 0.8 mm.; 
engorged, from 3 by 2.1 by 1.3 mm. to 4.8 by 3.3 by 2 mm. Color, 
unengorged, reddish brown; engorged, dark bluish gray. Capitulum 
0.336 mm. long (from tip of palpi to base of emargination of scutum) ; 
scutum 0.550 mm. long by 0.554 mm. wide. 
Larva (Pl. XIV, figs. 2, 4) —Unengorged, from 0.631 by 0.387 mm. 
to 0.703 by 0.445 mm.; engorged, from 1.28 by 0.76 mm. to 1.43 by 
0.85 mm. Color, unengorged, yellowish brown; scutum darker to- 
ward posterior end; engorged, slate-blue. Capitulum 0.139 mm. 
