INSECT ENEMIES OF LIVE STOCK 179 



on meat that is rendered unfit for human consumption, or at 

 any rate much depreciated in value, and to the dairy farmer 

 in the reduced milk yield of afflicted animals, and we obtain, 

 in England alone, an aggregate loss, caused by warble flies, 

 that has been variously estimated at from 2,000,000 to 

 7,000,000 per annum. Curiously enough, despite the enor- 

 mous loss which these flies entail, there are many points 

 in their life-histories that require elucidation. 



Vallisnieri, in 1710, appears to have been the first 

 observer of warble flies. Little is known of the adult, but 

 its long, elliptical, flattened eggs are white in colour, except 

 for a brown appendage, which serves the purpose of attach- 

 ment to the hair of the host. Horses, asses, and occasionally 

 men have been attacked. The whitish, transparent larvae 

 are comprised of twelve segments, and possess a pair of 

 very minute, crescent-shaped mouth parts. They are armed 

 with sixteen short, transverse bands of exceedingly minute 

 prickles, arranged in alternate narrow and broad stripes. 

 At a later stage, in Hypoderma lineata at any rate, the 

 larvae become quite smooth, except for a few prickles at 

 either extremity, and the mouth parts become more con- 

 spicuous. As they become older, they lose their worm-like 

 appearance and become spindle-shaped, with an extensive 

 armature of prickles on the ventral surface and a pair of 

 short, horny, blunt, projecting tubes or spiracles at the 

 hinder end. During the last stage of their development the 

 maggots become oval, compressed, and warty. Their skins 

 are much thickened, and they develop a powerful coat of 

 subcutaneous muscles. The armature of prickles becomes 

 more formidable than ever, and the hard tips to the 

 spiracles, at the hinder end of the body, are replaced by a 

 pair of kidney-shaped structures, sunk in oval depressions. 



At one time it was believed that the eggs were always 

 attached to the backs of cattle, on either side of the spine, 

 and that the larvae penetrated the skin soon after they 

 emerged. Another belief was that the mother fly herself 



