Tick species having marked host predilections may occupy the 

 same geographic area as the favorite host or only a certain seg- 

 ment of the host range; for example, H. houyi appears to be pres- 

 ent in most areas where its favorite "Host, tne groiind squirrel 

 Euxerus erythropus, occvirs. On the other hand, the elephant para- 

 site A. tholloni is not known from the northern and southern peri— 

 phery~of its host's range, the Varanus lizard parasite A. exorna. 

 turn does not follow its host into arid areas, and such Tiyrax para- 

 sites as H. bequaerti and its related species occiir in only a 

 restrictecf area of the host's range. 



Distributional data for most argasid species of the world are 

 extremely sparse due to the specialized and laborious techniques 

 necessary for collecting them. Even such a commonplace species 

 as that presently considered to be 0. moubata, long believed to 

 be well understood geographically, is now confused by a mounting 

 body of biological evidence that tends to discredit or at least 

 to iTiodify critically earlier impressions but is yet too limited 

 to be definitive. 



The number and variety of hosts an individual species uti- 

 lizes throughout its life cycle profouadly effects its distri- 

 bution and density. A single host tick such as B. decoloratus 

 that feeds on easily available herds or groups oT antelopes and 

 cattle is spared many of the dangers resulting from being for- 

 saken as a newly hatched larva or a newly molted nymph or adult 

 in an inhospitable environment where it must seek an entirely 

 different type of host for survival. It may thus become locally 

 numerous and also be carried afar by both wild and domestic hosts 

 under conditions frequently favorable for survival and reproduc- 

 tion. Similar l^A, a species that utilizes the same type of host 

 for all developmental sta>:es, even though it releases and re- 

 attaches two or three times, has advantages over one that cannot 

 survive unless a certain variety of hosts for nourishing the 

 different stages are present. 



The frequency with which immature stages of several African 

 amblyommas attack birds probably accounts in part for their 

 relatively wide distribution and population density. In semi arid 

 climes of North Africa and the Near East, where small mammals are 

 rare or localized, the great predilection of immature hyalommas 



_ 846 - 



