486 



The Warble Fly. 



[NOV., 



No. 21 {Warble Flies) ^ the life-history referring, however, to 

 Hypodenna lineata, while in Professor Ostertag's report bovis 

 is referred to. The following remarks are quoted from the 

 Leaflet mentioned : — 



"The damage caused by these pests is due both to the adult 

 flies and to their larvae or * bots.' The flies, when on the wing 

 and on the look out for a host on which to deposit their eggs, 

 frighten stock and frequently cause loss amongst 'in-calf cows 

 by making them stampede about the fields. The galloping about 

 is also bad for milch cows, not only because it affects adversely 

 the secretion of milk, but also because of the bruising of the 

 udders due to their striking against the body. The maggots or 

 ' bots ' living beneath the skin are a source of irritation to the 

 cattle, while there is also loss from hides ruined, by the perfora- 

 tions, for tanning purposes. They also cause loss to the butcher 

 who often finds the flesh beneath the ' warbled ' areas so altered 

 by the inflammation set up by the parasites that the beef in th'.it 

 region is spoiled. This so-called 'licked beef has a straw- 

 coloured, jelly-like appearance in a newly slaughtered carcase, 

 but turns to a dirty green in a few hours. 



" The life-history of Hypodervia Jineata is as follows : — The 

 fly deposits her eggs upon the hair of the beast, particularly on 

 the legs, just above the hoofs, whence a common name for this 

 fly in America — the heel fly ; but they are also placed elsewhere. 

 The eggs are fastened to the hairs, usually several together , 

 each egg is firmly attached to the hair by a process which clasps 

 the hair immediately the egg is laid by the fem.ale. The animal 

 licks the place where these e'.^^gs are placed, and the larvae hatched 

 from them are carried by the tongue into the mouth. The young 

 maggots, which are spiny, pass into the gullet or oesophagus and 

 soon penetrate its walls. They then moult their skin, becoming 

 smooth, and proceed to wander through the connective tissues 

 of the host and between the skin and flesh to the back, under 

 the hide of which they are at last found. Here they moult again, 

 once more becoming spiny. At this stage they comm^ence to 

 produce considerable irritation, and a swelling arises over them 

 — the warble — which soon becomes perforated by a hole at the 

 summit. The tail end is pointed towards this aperture, the two 

 spiracles or breathing pores situated on it being placed close to 

 the opening. There is now formed much pus, upon which, 



