168 



large, strong, and of unusual length, being sharply bent and provided 

 with an accessory tooth at the base. In the flattened head the eyes 

 are wide apart hi both sexes, so that the width of the front is of no 

 value for the distinction of males and females ; the antennae, which 

 are concealed in pits, are invisible from above, and so as a rule is the 

 proboscis ; the latter, which is curved and extremely slender, is 

 protruded when required for use from between a pair of prominent, 

 downwardly projecting, chitinous blades (the maxillary palpi). 

 Although the sexes (or at least males and non-pregnant females) 

 are closely similar as regards other external characters, the females 

 can usually be distinguished without any great difficulty, owing to 

 the presence at the tip of the abdomen in this sex of a median, 

 tongue-like, chitinous flap on the dorsal side ; this flap or lobe is 

 clearly shown in fig. 100, but since it sometimes stands up vertically, 

 close examination may be necessary in order to recognise it in dried 

 specimens. The males sometimes show at the tip of the abdomen 

 a protruding, curved, chitinous spine (part of the genital apparatus). 

 As regards dimensions, the species of Hippobosca vary from a 

 length of 5 or 6 mm. (wing-expanse 14-16 mm.) in the case of H. 

 capensis, von Olfers, to 11.5 mm. (wing-expanse 24 mm.) in that of 

 a female H. camelina, Leach, containing an adult larva ; it should 

 be noted that gravid females are subject to great variations in size 

 owing to the distension of the abdomen produced by the larva. 



Owing to the parasitic habits of the genus Hippobosca, the 

 distribution of many of the species, like that of Hippoboscidae in 

 general, is remarkably extensive, since the flies have often been 

 introduced with one or other of their hosts into new localities by 

 the agency of man. In addition to the three species represented on 

 Plate XIII., three others are also found. in the Ethiopian Region; 

 of these, the European Hippobosca equina, Linn., which is a parasite of 

 horses* and has been met with in Senegal and Cape Colony as well as 

 in Egypt, has doubtless been introduced with its host, as has happened 

 in other parts of the world. Hippobosca capensis, von Olfers (syn. H. 

 francilloni, Leach), which is the smallest species of this genus and 

 was originally described from a specimen from the Cape of Good 



* H. equina also occurs locally on cattle. 



