OESTRIDAE BOT-FLIES 



515 



which the larvae are to draw their nutriment, but others place 

 their larvae, already hatched, in the entrances of the nasal 

 passages. They do not feed on the blood or tissues of their 

 victims, but on the secretions, and these are generally altered or 

 increased by the irritation induced by the presence of the un- 

 welcome guests. It would appear, on the whole, that their presence 

 is less injurious than would be expected, and as they always quit 

 the bodies of their hosts for the purposes of pupation, a natural 

 end is put to their attacks. We have ten species in Britain, the 

 animals attacked being the ox, the horse, the ass, the sheep, and 

 the red deer ; others occasionally occur in connexion with animals 



FIG. 245. Cephalomyia maciilata, a Bot-fly of the camel. Arabia. A, The fly with 

 extended wings ; B, under aspect of the head : a, antenna ; b, the obsolete mouth-parts. 



in menageries. The eggs of Gastrophilus equi are placed by the 

 fly, when on the wing, on the hair of horses near the front parts 

 of the body, frequently near the knee, and, after hatching, the 

 young larvae pass into the stomach of the horse either by being- 

 licked off, or by their own locomotion : in the stomach they be- 

 come hooked to the walls, and after being full grown pass out 

 with the excreta : the Bots as these larvae are called are some- 

 times very numerous in the stomach, for a fly will lay as many 

 as four or five hundred eggs on a single horse : in the case of 

 weakly animals, perforation of the stomach has been known to 

 occur in consequence of the habit of the Bot of burying itself to 

 a greater or less extent in the walls of the stomach. Hypoderma 

 bovis and H. lineata attack the ox, and the larvae cause tumours 

 in the skin along the middle part of the back. It was formerly 



