154 
Biology of Dermacentor 
have a more or less decided tendency toward a dorso-posterior pro¬ 
longation ; the scutum of this species is banded with white, but these 
markings are often yellowish and not intense. 
In the group which moults off the host we find hunteri, parumapertus, 
parumapertus var. marginatus, veniistus, occidentalis and variabilis. In 
all but variabilis the stigmal plates have a prominent dorso-posterior 
prolongation, and the goblets are numerous and much smaller than in 
members of the previous group. D. variabilis has broad stigmal plates, 
with a short, broad dorso-posterior prolongation and many exceedingly 
small goblets. All of the species in this group except parumapertus 
have extensive, inteuse white markings on the scutum. 
Economically this genus is of considerable importance in the United 
States, as all of the species are of some economic significance except 
D. parumapertus, D. parumapertus var. marginatus, and D. hunteri. 
The first two ticks have not been found to attack any host other than 
rabbits, and the last has been taken only on the mountain sheep. 
D. variabilis is of little economic importance, so far as known, because 
among the domestic animals it most commonly attacks the dog. 
However, it is sometimes taken on the larger domestic animals and 
occasionally attaches itself to man. D. occidentalis and I), venustus are 
common pests of man and nearly all domestic animals, and the latter 
species, as is well known, is the transmitter of the disease of man 
called Rocky Mountain spotted fever. The other three species— nitens, 
albipictus and nigrolineatus —are each of considerable importance as live 
stock pests; none of these are known to attack man. 
The life histories of all of the previously mentioned species (except 
D. parumapertus proper) have been worked out during the investigations 
conducted by the Bureau of Entomology. The more important facts 
thus obtained, appertaining to the distribution, life histories and habits 
of nitens, occidentalis, parumapertus var. marginatus, variabilis and 
venustus have been published 1 . 
1 Hunter, W. D. and Hooker, W. A. Information concerning the North American 
fever tick, with notes on other species. Bull. 72, Bureau of Entomology, U.S. Dept. Agr. 
pp. 49-52, 1 pi. 2 figs. Nov. 2, 1907. 
Hunter, W. D. and Bishopp, F. C. Some of the more important ticks of the United 
States. Yearbook, U.S. Dept. Agr. for 1910, pp. 225-228, 1 pi. 1911. 
Hunter, W. D. and Bishopp, F. C. The Rocky Mountain spotted fever tick. Bull. 
105, Bureau of Entomology, U.S. Dept. Agr. 47 pp. 3 pis. 3 figs. Nov. 17, 1911. 
Hooker, W. A., Bishopp, F. C. and Wood, H. P. The life history and bionomics of 
some North American ticks. Bull. 106, Bureau of Entomology, U.S. Dept. Agr. pp. 21-37, 
70-71, 158-204, 5 pis. 5 figs. Sept. 7, 1912. 
