Diseases, Ticks, and their Eradication. 147 



aud therefore harmless. The former condition explains the reason of 

 the constant infection of African veld by redwater, biliary fever, and 

 gall-sickness. The animal which recovers from the disease continues 

 to act as a host for the ticks. The ticks become infected with the 

 parasites, and in turn carry them back to the animal. In this way a 

 circle is formed between the animal, the micro-organism of the 

 disease, and the tick. The tick and micro-organism are dependent on 

 the animal; without it their life-cycle would come to an end. They 

 require the hosts for the multiplication of the species. Accidentally, 

 through the invasion of a great number of parasites such an animal 

 becomes sick and may die. An adaptation between the host and the 

 micro-organism has resulted. The hosts act as virus reservoirs. Both 

 seem to benefit from this infection — the animal with its immunity 

 and the parasite with a permanent home. It is evident that diseases 

 caused by blood parasites and transmitted by ticks would disappear if 

 we were able to break the life-cycle of the parasite. It must reason- 

 ably be expected that the easiest way to achieve this is to attack the 

 tick ; to attack it successfully the method to be adopted must be based 

 on its life-history, which has to be explained. 



Ltfe-iiistory or the Ticks. 



The ticks belonging to the order of Acarina are easily recognized 

 by the naked eye. They possess flat bodies when not engorged, or 

 they are more or less swollen when engorged with blood. We dis- 

 tinguish males and females in the adult stages. The body of the male 

 is always flat, whereas the female engorges and ctows in size ; in this 

 country the latter is usually known as the tick proper. Male and 

 female meet on an animal for copulation, and as soon as the fertiliza- 

 tion has taJven place the female engorges. Underneath this engorged- 

 female the male can usually be found. Before repletion the female 

 is about the same size as the male. The presence of the small tick 

 underneath the female, especially in the case of the blue tick, has led 

 to the poipular opinion that this is a young one. After the female 

 has repleted herself she drops and hides in the grass or in the sand, 

 and soon after begins to lay eggs. The process of oviposition varies 

 in length of time according to the season in which the ticks drop. 

 After a lapse of a certain period the eggs begin to hatch and the 

 young larvae, commonly known as seed ticks, appear. They seek 

 their way to the top of the grass or bushes, from which they attach 

 themselves to a suitable host which may be passing. So far the ticks 

 with which we have to deal behave similarly, but the various species 

 differ in their habits, and according to these l-obits we can divide 

 them into three groups. 



Firstly. — The ticks which, for the completion of their life-cycle, 

 require only one host. To this group belongs the blue tick (Boophilus 

 decoloratus). It reaches the host as a larv^a ; it moults (changes its 

 skin) on the animal from the larval into the nymphal stage, and again 

 from the nymphal to the adult stage. In the adult stage the sexes 

 meet again and the life-cycle begins afresh. 



Secondly. — Ticks which require two hosts for the completion of 

 their life-cycle. To this group belongs the red-legged tick (Rhipice- 

 phalus evertsi). It comes as a larva, it moults into the nymphal 

 stage, and leaves the animal as an engorged nympha. The moulting 



