168 INSECTS AND MAN 



But we are here concerned with the ticks as disease- 

 carriers, and it is by their agency alone that piroplasmosis 

 in cattle is spread from host to host; without the ticks 

 there would be no red water, Texas fever, or tick fever, 

 call it what you will ; a tick of some species or other is as 

 necessary in the propagation of the disease as mosquitoes 

 are essential to the spread of malaria or yellow fever. 

 Realising the importance of this fact, the American Bureau 

 of Animal Industry, by vigorous eradication work, for the 

 six years 1906-1912, rendered 162,648 square miles tick- 

 free, which is equivalent to saying that this enormous area 

 was immunised from Texas fever. The total annual loss, 

 due to ticks, has been estimated, in America alone, at from 

 $40,000,000 to $100,000,000, and is comprised of direct loss 

 by death of cattle suffering from tick fever, losses owing 

 to arrested growth of infected animals, which lessens beef 

 and milk production, expenses of fighting the fever-bearing 

 tick, etc. In short, these ticks have a detrimental effect on 

 the whole of the agriculture of the Southern United States. 



In America the tick, Margaropus annulatus, is the 

 vector of piroplasmosis in cattle ; in Australia the vector is 

 Margaropus annulatus australis (fig. 46) ; and in Africa 

 Margaropus annulatus decoloratus is mainly concerned in 

 the spread of the disease, though two other ticks, Hyalomma 

 cegyptium and Hcemaphysalis punctata, are also respon- 

 sible for its spread. In Norway, and certain parts of Europe, 

 the tick, Ixodes hexagonus, is an essential factor in the 

 transmission of red water ; and in other parts of Europe, 

 including the British Isles, a closely related species, Ixodes 

 ricinus, carries the blood parasite from host to host. 



It is hardly necessary to describe all these ticks and 

 their life-histories; systematic descriptions can be found 

 in many books, and the life-histories have, in some cases, 

 not been fully worked out. Margaropus annulatus, how- 

 ever, is practically cosmopolitan, and its life-history may 

 be taken as typical. From what has been said, it will 



