112 



of which by attacking and preying upon " favoured hosts " of Tsetse- 

 flies may, in certain localities and under certain conditions, have a 

 distinct controlling effect on the range and increase of the latter. Thus 

 Fiske (54), writing with reference to G. palpalis on islands in and also 

 on the mainland of Lake Victoria, Uganda, states that the " Leopard 

 is of very great importance in the bionomics of tsetse as a deprivative 

 enemy, for it is a major factor in controlling the range and density of 

 bush-buck, situtunga, bush-pig and perhaps other hosts of the fly." 

 In a subsequent section of his paper the author furnishes detailed 

 evidence in support of this statement, concluding by remarking with 

 regard to the mainland : " There would be inland extension of 

 infestation to approximately five times its present depth at many 

 points, and along extensive reaches of mainland shore, if it were not 

 for the deprivative effect of the activities of leopards. They are 

 certainly a more efficacious natural enemy of the tsetse than spiders, 

 or than any other destructive enemy that has been identified/' 



Fiske also shows that onslaughts upon host animals by species of 

 Tabanus, of whose bloodthirsty attacks the larger African antelopes 

 are well-known to be intolerant, are inimical to G. palpalis. "It is 

 not necessary," writes the author, " that the host animals shall be 

 destroyed in order to injure the fly; but it is quite sufficient that they 

 should move a little outside the range or reach of flies from either 

 shelter or breeding places. 



" Therefore if the animal is induced by Tabanus, or any other biting 

 fly, to move a little farther away from the specifically protected 

 precincts, Glossina is forced to follow, and in following is exposed to 

 all the risks, and enemies of a destructive nature, that make specific 

 protection a requisite for its existence. The effect of the rival is 

 precisely equivalent to either of the following : (a) reduction in 

 quantity of available food, (b) reduction in quantity or degree of 

 protection, or (c) increase in number or destructiveness of enemies. 



" This is if the host is induced to leave the locality. It is the same 

 if retaliatory activities on the part of the host induce the flies to desist 

 from attack and to move on in search of another, more submissive 

 animal. To do this the flies must leave protected precincts and undergo 

 greater risk of being destroyed themselves, or of being unable to find 

 protection for their young. 



" The activities of Tabanus have the direct effect of reducing the 

 quantity of available food in protected precincts, which is the equiva- 

 lent of either reducing the amount of degree of protection, or increasing 

 the number or destructiveness of enemies." 



The species of Glossina are subject to the attacks of natural enemies, 

 which serve to prevent excessive increase ; these enemies appear to be 

 of various kinds and fairly numerous, and it is as well that we should 

 be familiar with them. We have collected together certain statements 

 relating thereto, scattered through papers by different authors, which 

 have been published in recent years. 



The enemies of Tsetse-flies like those of any other harmful species 

 of animal may be grouped into two main categories : predatory 

 animals and parasitic organisms. 



The former do not confine their attacks to any particular species, 

 but prey indifferently upon a very large number. Being themselves 

 relatively far from numerous, all that they can do is to keep the increase 

 of noxious animals within certain limits. Parasitic organisms, on the 

 contrary, are for the most part highly specialised, having each a single 



