158 LIFE HISTORY OF NORTH AMERICAN TICKS. 
and adults were much more troublesome. While the itching was 
intense, none of the points of attachment became infected and there- 
fore soon healed. In one case a nearly fully engorged larva was found 
under the knee, which certainly had not been attached more than 
36 hours. Hunters and others who have occasion to spend consid- 
erable time in the forests complain a great deal of the attacks of this 
tick. Schwarz and Bishopp heard of one man whose legs were well 
covered with suppurating sores and who was ill from the attack of 
these ticks and the wounds produced by scratching. At Victoria, 
Tamaulipas, Mex., on December 9-10, a much smaller number of ticks 
were found; no larve were seen and horses were only lightly infested. 
The Bureau of Entomology has received large numbers of males 
of this species from the Guinand Brothers of Caracas, Venezuela, 
with the statement that they are the source of great loss to the cattle- 
men in that country. 
NATURAL CONTROL. 
No observations of natural enemies of this species have been made 
by us. Newstead (1909) records the finding of engorged females in 
the stomachs of the tinkling grackle (Quascalus crassirostris). He 
also observed parrot-billed blackbirds picking ticks, probably of this 
species, from the heads of horses. 
ARTIFICIAL CONTROL. 
As with americanum the large number of hosts which this species 
has and the long periods which they can live without a host pro- 
hibit successful control by pasture rotation. Dipping, mopping, or 
handpicking must be resorted to when the species becomes a pest. 
Dipping as often as every 8 days would be required in order to prevent 
the dropping of engorged adults. 
Genus DERMACENTOR Koch. 
Five of the nine species of the genus Dermacentor which occur in 
the United States have been studied and are here considered. One 
species, Dermacentor venustus, has also been studied by Ricketts and 
by Cooley. This latter species is the only member of the genus that 
has been shown to transmit disease. 
Two different types of life history were found to occur in the genus. 
While 4 of the species studied, namely, occidentalis, parumapertus 
var. marginatus, variabilis, and venustus drop to pass both molts 
off the host, nitens does not do so but transforms upon the host. 
Another species (Dermacentor albipictus) which is now being studied 
has also been found to have this habit. This habit of molting upon 
the host, as well as the preference shown by Dermacentor nitens for 
the inside of the ears as a place of attachment, where it is consider- 
ably protected from bird and other enemies and where it is not 
readily removed by the host, must be considered as protective adapta- 
tions. The adults of all species of this genus which we have studied 
