112 



The ticks are especially common at the beginning of summer, when 

 the heat and moisture required for their development are present. 

 The greater the altitude and the more bare the soil, the fewer ticks 

 there will be, but M. anmdatus, the commonest tick of South Africa, 

 had been found at all altitudes ; Rhipicephalus evertsi is much less 

 common and R. appendiculatus is rarely met with on elevated plateaux, 

 but it is specially found in valleys where the vegetation is abundant. 

 Rhipicephalus simus and Amblyomma hebraeum are chiefly found on 

 broad sandy plains covered by a scanty vegetation. It has been 

 noticed that the number of ticks increases proportionally with the 

 number of head of cattle, and apart from their capacity for transmitting 

 disease, they are very harmful to cattle in consequence of the quantity 

 of blood which they extract. It has been calculated that in one year, 

 the ticks on one beast are capable of removing 48 litres of blood and 

 some ticks are capable of drawing as much as 2 cubic centimetres. 

 Theiler mentions the case of a horse which died of acute anaemia as 

 the consequence of an extraordinary attack by 31. decoloratus. The 

 ticks collected from this animal weighed 20 kilos (44 lb.). The 

 eggs were unharmed under 4 months' exposure to a temperature of 0° C, 

 and the same temperature does not kill either larva, nymph or adult. 

 Prolonged immersion in water apparently has little effect upon them. 



The author divides the ticks into 3 classes, according to whether they 

 require one, two, or three hosts to complete their life-cycle. He says 

 that the important facts to be known in the hfe-history of the tick are 

 the dates of oviposition and hatching ; the time required to complete 

 the Ufe-cycle on the host ; the time that larva and nymph remain upon 

 the host, and the time required by them, after quitting their 

 host, to complete their respective metamorphoses ; the time 

 required by the female to gorge and detach herself ; and lastly, the time 

 that the larval, nymphal, and adult forms can survive. 



The author then proceeds to deal with the life-history of the following 

 ticks. 



Margaropus annulatus var. decoloratus. This tick requires one 

 host and takes 3 weeks to pass from larva to adult ; after 3 weeks 

 the gorged females commence to quit their host and by the fourth 

 week all have done so. Five days after this, the female oviposits — 

 at all events in the hot season. In summer, the eggs hatch in from 

 3 to 6 weeks, taking longer in winter. Young larvae kept in the 

 laboratory may live as long as six months. In the open they station 

 themselves on a plant and wait for a host. They do not feed on the 

 juices of plants and perish if, after six months, they fail to find a host. 



Rhipicephalus evertsi requires 2 hosts. In summer the eggs hatch 

 30 days after oviposition. The young larvae can live 7 months without 

 food. They become nymphs on their host and these are found close to 

 the point to w^hich the larva was attached. The nymph falls off in from 

 16 to 21 days, moulting to the adult stage requires 24 days and the 

 adult gorges itself and falls to the ground in from 6 to 10 days and is 

 capable of living for a whole year on the soil apart from a host. 



Rhipicephalus appendiculatus, capensis, nitens. These ticks require 

 3 hosts, the adult females gorging themselves in 4 days. The eggs hatch 

 in the warm season in about 28 days, or several months in winter. 

 Sixteen to twenty days later the larva becomes a nymph. In the 

 laboratory the larvae have been kept for 7 months and nymphs for 6 



