THE ACAEINA OE MITES. 



67 



Fig. 125.— Tarsus IV of Ambhjomma. (Original.) 



at articulations. The cause of Texas fever is a minute protozoan parasite, Babesia 

 bigemina. This is taken up with the blood of Margaropus, which then inoculates 

 each animal that it attacks. And even the young that have not infested any animal 

 may produce the disease. The young ticks (fig. Ill), called "seed ticks," are born 

 on the ground; they climb upon grasses or bushes and await the coming of cattle. 

 Each attaches itself at the first opportunity and begins to draw blood. In about a 

 week it molts, remaining on the host 

 during this period. The male increases 

 but little in size, but the female becomes 

 enormously swollen and in about a month 

 she is ready to drop off and deposit eggs 

 (fig. 113). Young or "seed ticks" of the 

 cattle tick may live several months with- 

 out food, and even remain alive when 

 submerged in water for 3 months. The adults can Hve for long periods without food, 

 but probably not as long as the argasids. Once in the blood of cattle the parasite 

 destroys the red blood corpuscles and causes a thinness of blood, the haemaglobin 

 of which appears in the urine. After death the spleen and liver are found to be 

 greatly enlarged. The most promising preventive seems to be the removal of cattle 

 from pasture for one year. This pasture disinfection may be hastened by cultiva- 

 tion for one year, or grazing it to sheep. It has been noticed that southern cattle may 

 become immune, and with this hint a method of vaccination was 

 devised for treating northern cattle when taken south. 



A variety of the cattle tick ( M. annulatus var. australis Ful- 

 ler) has a posterior median projection to the body; it occurs in 

 tropical regions, and also transmits Texas fever. 



The typical species ( Margaropus uinthemi Karsch) and an Afri- 

 can species have the hind pair of legs enormously enlarged in 

 the males. Forms closely related to M. annulatus Say (sub- 

 species or perhaps distinct species) occur in South America, 

 South Africa, and Australia, and are concerned in the dissemina- 

 tion of the Texas fever, often called "red water." The genus 

 was formerly knoAvn as Bbophilus, but B. annulatus is congeneric 

 with the type of the earlier Margaropus. There are several other 

 species of ticks found on cattle, but none is known to carry the 

 parasite of Texas fever. 



Of Dermacentor (fig. 116) there are 9 species in this country, 

 most of them with the scutum more or less variegated with white and brown. The 

 common one is the "dog tick," Dermacentor variabilis Say (figs. 114, 115), and is our 

 most widely distributed species. It is found on cattle, dogs, horses, rabbits, and 

 sometimes on man. On the latter it causes no serious consequences, but is a source 

 of much irritation. They are so tightly attached that it is often impossible to remove 

 them without either leaving the head in the flesh or else tearing out a piece of the skin. 

 D. occidentalis Neumann is common in California and often taken on deer. It is 

 less marked with brown than our other forms, and the white has a more waxy appear- 

 ance than in our eastern D. variabilis. 



D. parumapertus Neumann, from California and Arizona, and D. nigrolineatas Pack- 

 ard, from the Northern States, are species without marks on the shields; the former 

 attacks mostly small animals, as jack rabbits; the latter is usually on deer or allied 

 mammals. 



The Dermacentor venustus Banks, which occurs in the Northwest, is the carrier of 

 the Rocky ^lountain spotted fever, a serious disease of man. The disease ^ apparently 

 occurs naturally in certain spermophiles inhabiting that region, and has been especially 



Fig. 126.— Shield of 

 Haemaphysalis chor- 

 deilis, female. (Orig- 

 inal.) 



Produced by Babesia hominis. 



