addition to such extrinsic environmental factors as physical bar- 

 riers, temper atvire, and humidity. For ectoparasites that com- 

 monly attack both wild and domestic animals a double set of 

 values needs be employed. 



The distribution of parasites that utilize widely differing 

 hosts in each developmental stage is effected not only by the 

 physiological range tolerable to the ectoparasite but also by 

 that tolerated by the several types of hosts required to complete 

 the life cycle. In families of insects consisting of many spe- 

 cies certain basic distributional patterns are more easily dis- 

 cerned than in the family Ixodidae composed of relatively few 

 species variously adapted to a wide range of environments and 

 hosts. 



In Africa and in the Sudan in particular, where both domes- 

 tic animals and many wild animals make long migrations in search 

 of water and grazing, particiilar caution should be exercised in 

 geographic evaluation of collections consisting only of male 

 ticks, which remain attached to the host for many months. Males 

 may be unaccompanied by females, which generally feed for four 

 to ten days, either because the reproductive season is not yet 

 at hand or because they have been transported far beyond their 

 normal range by hosts wandering in search of food and water. 

 When outside their normal geographic range, these unassociated 

 males are not only false zoogeographic indicators but of re- 

 duced epidemiological significance since they do not normally 

 leave the host and attach to another. Inasmuch as domestic 

 animal parasitizing ticks are frequently those also directly 

 or indirectly associated with human diseases these considera- 

 tions assume additional importance. 



The wide disparity in size and beauty between different 

 species of ticks as well as in degree of exposure or conceal- 

 ment of feeding sites on the host may give a false distribii- 

 tional picture v;hen collections are gathered haphazardly and 

 by nonspecialists. 



It goes without saying that in great areas of the world 

 and especially in the Sudan, remoteness of considerable areas 

 and lack of general and specialized interest by collectors may 

 often result in skewed data or samplings that are far from 

 homogenous. 



- 8/V5 - 



