150 Journal of the Department of Agriculture. 



about twenty-five days as a minimum and 160 days as a maximum. 

 The adult female drops from about the tenth to the twentietli day 

 after attaching-. Adults have been known in our experiment to live 

 up to a period of seven months. This tick is known to produce severe 

 ulcerating sores on the place of its attachment, and is frequently 

 responsible for the loss of one or more teats. 



The Dog Tick (Haemaphysalis leacTii). — The female begins to lay 

 eggs three to seven days after it has left the host. The period varies 

 according to the season in which it drops. The eggs require about a 

 month to hatch. The young larvae remain on their host for n period 

 of two to seven days. When engorged they drop to the ground and 

 moult into nymphae. In about a month's time the nymphae seek a 

 host and remain on it for two to seven days, and then drop engorged 

 to the ground ; they change into adults in about ten to fifteen days. 

 The female adult requires about ten to fifteen days for repletion. 



The Striped-leg Tick (Bontpoot) (Hyalomma aegj/ptium). — 

 Though not a disease-transmitting tick, it frequently is the cause of 

 lameness in sheep and goats, the adult attaching itself between the 

 hoofs; it is sometimes known to produce ulcerating sores in cattle. 

 Only adults are found on domesticated animals, the larval and 

 nymphal stage are passed on different smaller wild animals, including 

 birds. 



The Sheep Paralysis Tick (locodes pilos'us). — The life-history of 

 this tick has not yet been studied. 



The Spinose Ear-tick. — It has been known in South Africa 

 since 1910, and was probably introduced from America. It 

 is a tick which thrives best in dry areas, hence its 

 prevalence is recorded • in the Karroo and western South 

 Africa. It is not known to transmit n definite disease, but 

 its presence is decidedly harmful. The death of calves, sheep, 

 and goats has been put down to its effects. The female ticks lay 

 their eggs in sheltered places. The eggs hatch out in twenty-four to 

 fifty-six days. The young larvae after reaching a suitable host settle 

 in the ears. A larva can live about two to four months without 

 feeding. The larvae engorge in five to seven days and then moult 

 into nymphae. These engorge themselves after about one week, but 

 they can remain for many weeks and months before they finally 

 engorge and leave the host. The engorged nymphae drop off the host, 

 crawl into a sheltered place, where they moult into adults after from 

 seven to thirty-five days. They are then fertilized by the males and 

 subsequently lay eggs. The adults can live for a long time. Megnin 

 states tliat he kept some alive for two years. 



Transmission op the Disease. 



From the life-history, as outlined above, the following possi- 

 bilities may be observed in the transmission of a disease: — 



Firstly. — The transmission is effected by means of young larvae 

 whose mothers have been sucking blood from infected animals. This 

 has been known to be the case in redwater, spirochaetosis, and anaplas- 

 mosis. It is the principal mode of propagation of redwater by the 

 blue tick; the larvae of the brown tick may transmit redwater, and 

 the larvae of the red tick have proved to be hosts of spirochaetosis. 



Secondly. — The transmission is effected by one of the succeeding 

 stages, either by the nymphae which infected themselves as larvae or 



