484 



The Warble Fly. 



[NOV., 



Professor Ostertag adds others, remarking that the carrying out 

 of such a law would occasion hardships which stand in no 

 relation to the desired end ; his chief objection, however, lay in 

 a belief that compulsory measures would accomplish less than 

 voluntary action, for the carrying out of regulations could 

 not take place without powerful machinery of an administrative 

 character. For such reasons Professor Ostertag did not consider 

 legal action was advisable, but believed in encouraging voluntary 

 efforts. In the course of remarks on the harm done, he stated 

 that according to Kiihnau the loss owing to cutting away of 

 affected flesh may be between los. and 30s. per head. According to 

 Horne, whole carcases may have to be destroyed and lost to the 

 trade if the larvae in wandering from the spinal canal to the hide 

 leave dirty-green coloured passages behind them. Director 

 Ruser, of the slaughter-house at Kiel, estimated that 40 to 

 50 per cent, of all the Holstein cattle which were at pasture 

 were affected with warbles, and according to the returns of the 

 dealers in hides and the tanners, one-fifth to one-seventh of 

 all cattle slaughtered in Germany are warbled. 



The attacks of warble flies appear to be unknown where the 

 cattle do not go to pasture until mid-day, and this is usual in 

 most districts of South Germany. This is believed to be largely 

 due to a biological peculiarity of the larvae, which leave the warbles 

 from early morning up to 8 a.m., and if the cattle still remain in 

 the sheds the larvae fall on the floor of the cowsheds and are 

 destroyed. The warble fly only occurs naturally in places where 

 the cattle are at pasture from spring onwards both day and night, 

 or where they are driven to pasture in the early morning. To 

 combat the pest then, the life-history, which the warble fly accom- 

 plishes as an independent insect and as a parasite, must be 

 interrupted. It has been recommended to rub the cattle with 

 some evil smelling material at the time of egg-laying in order to 

 keep off the flies. Professor Ostertag for several reasons does 

 not approve of this procedure, and says that no case is known to 

 him where good results have been attained by this method. The 

 only useful means of combating the pest is to extract the 

 immature bots from the warbles and destroy them. This may 

 be done by opening the warbles with a sharp knife and remov- 

 ing the bots ; the scar in the hide will heal over smoothly and 

 loss will not occur as is the case when the bots themselves drill 



