190 LIFE HISTORY OF NORTH AMERICAN TICKS. 
of that disease. The use of the name was due to confusion regarding 
the identity of the tick Dermacentor venustus, which is the known 
transmitter of this disease in nature. 
NATURAL CONTROL. 
No natural enemies of this species have been observed by the 
writers. However, it is probably subject to the attack of the various 
predaceous enemies of other tick species. McAtee (1911a) states that 
ticks of this species have been found to be eaten by the dwarf hermit 
thrush (Hylocichla guttata nana). 
ARTIFICIAL CONTROL. 
The comparatively short longevity of the larve and nymphs of 
this species indicates that it may be possible to practice the rotation 
method of eradication. This method appears to be more promising 
than the use of dips on account of the fact that the engorgement 
period of the immature stages is quite short and usually takes place 
on small wild mammals. The occurrence of the species throughout 
the year is also an obstacle to the practice of dipping or mopping 
animals with tickicides. 
THE AMERICAN DOG TICK. 
Dermacentor variabilis (Say). 
The common name of this tick is given it because in this country 
it is the most widely distributed species which commonly attacks 
the dog. 
DESCRIPTIVE. 
Adult (Pl. XV, figs. 5-11).—Males from 3.5 by 2.5 to 4.5 by 2.5 mm. 
Females, unengorged, about 3.75 by 2.25 mm.; engorged, 10 by 7 by 5 
to 15.5 by 11.2 by 7.4mm. Male reddish brown, dorsum with irreg- 
ular white marks; female reddish brown, scutum with a white band 
on the lateral margin, broadening posteriorly; a brown marginal 
stripe near each eye and sometimes two white median stripes. 
Nymph (Pl. XV, figs. 2-4)—Unengorged, about 1.5 by 1 mm.; 
engorged, 3.5 by 2 by 1mm. to 4.by 3 by 2 mm.; average 3.5 by 2.5 
by 1.5 mm. Color, unengorged, pale yellowish brown; posterior 
margin of scutum dark brown, lateral margins of scutum with brick- 
red markings; in living specimens the intestines are visible as brown 
bands through the body walls; engorged, slate-gray. Capitulum 
0.287 mm. long (from tip of palpi to base of emargination of scutum); 
scutum 0.488 mm. long by 0.526 mm. wide. 
Larva (Pl. XV, fig. 1)—Unengorged, about 0.60 by 0.35 mm.; 
engorged, 1.5 by 1mm. Color, unengorged, pale yellow; lateral 
margins of scutum brick-red; engorged, dull gray. Capitulum 0.17 
