178 INSECTS AND MAN 



the mouth and gullet. Soon, however, the maggot passes 

 into its host's stomach and undergoes considerable change 

 in appearance. Near its mouth are a number of hooks : 

 with these it fixes itself firmly to the stomach wall. Its tail 

 end becomes broadened, and the two spiracles, or respiratory 

 organs, which appeared as two flap-like projections in the 

 earlier stage, are drawn somewhat within the body and 

 protected by a horny plate ; at the same time the segments 

 become spiny. The larvae attain their full growth in the 

 spring, and then they are from three-quarters to one inch 

 in length. Their nutriment is derived from the tissues to 

 which they are fixed, and also from the stomach contents, 

 and in this respect it is of interest to note that they are 

 generally found clustered round the opening of the stomach 

 into the intestine, thereby, as it were, damming up the con- 

 tents, with the object of obtaining more food. When fully 

 grown, the bots relax their hold, pass through the intestine, 

 and escape with the excrement, when they burrow into 

 the ground to pupate. The pupal stage usually lasts from 

 thirty to forty days, and the newly emerged fly at once 

 proceeds to the business of providing another generation. 



According to some authorities, the bots do little harm to 

 a horse ; others assert that they are very dangerous, by 

 causing great irritation in the stomach and intestines, by 

 absorbing food material, which could be more profitably 

 employed, and by causing an obstruction to the free passage 

 of food along the alimentary canal. Harmful or not, the 

 fact remains that nine-tenths of all horses pastured in the 

 summer become attacked, and the proportion of those in 

 work is somewhat smaller. 



The ox warble flies, Hypoderma bovis (fig. 49) and Hy- 

 poderma lineata, are the cause of extensive loss to stock- 

 owners in this country, whilst the latter is a well-known 

 pest in America. The loss in damaged hides alone, in 

 Manchester, Newcastle, and Nottingham, in a single year, 

 was estimated at 33,715 ; add to this the loss to the butcher 



