ACABINA 



447 



or more or less reetangriilar and up to 13 mm. long and yellowish or 

 slate-color in the female: southern states, on cattle, often very common, 

 causing the destructive Texas fever, the disease being caused by the 

 inoculation of the cattle by the tick of Babesia higemina, a sporozoan 

 blood parasite (see page 47). 



4. Dermacentor Koch. Eyes present; pedipalps short and broad; 

 stigmal plate comma-shaped; scutum partially white or yellow: 20 

 species, about 4 American. 



D. variabilis (Say) {D. electus Koch). Dog tick (Fig. 702). Body 

 oval or rectangular; scutum reddish-brown with white spots; stigmal 



Fig. 701 Fig. 702 



tig. 701 — Margaropus annulatus (Banks). A, female; B, male. Fig. 702 — Derma- 

 centor variabilis — male (Banks). 



plate finely punctate; color brown, variegated; length of replete female 

 15 mm. ; breadth 9 mm. : on domestic animals and man, often abundant 

 in the eastern and central states, being the tick that often attaches to 

 persons in the woods. 



D. venustus* Banks. The Rocky Mountain spotted-fever tick. Body 

 an elongated oval and 2 to 6 mm. long in the male and about 15 mm. 

 long in the female and reddish-brown in color: the northwestern states; 

 the larvae live on small mammals and the adults on the larger domestic 

 animals and man; the cause of a very dangerous fever which is the result 

 of the inoculation by the tick of a sporozoan blood parasite, Babesia 

 hominis (see page 47). 



Family 10. HYDRACHNIDAE.t 



Fresh-water mites. Body usually ovoid or spherical and sometimes 

 of large size, and often brightly colored; 1 or 2 pairs of eyes present; 



* See "A Zoological Investigation into the Cause, Transmission, and Source of 

 Rocky Mountain Spotted Fever," by C. W. Stiles, Bull. No. 20, Hj'g. Lab., Treasury 

 Department, Washington, 1905. 



t See "Nordamerikanische Hydrachniden," by F. Koenike, Abh. d. natur. Ver. zu 

 Bremen, Vol. 13, p. 167, 1895. "Deutschlands Hydrachniden," by R. Piersig, Bibl. 

 Zool. No. 22, 1897 to 1900. "Hydrachnidae und Halacaridae," by R. Piersig und 



