402 MANAGEMENT AND FEEDING OF SHEEP 



caution should be taken to make sure that the sheep 

 brought in are healthy. 



Grub in the head (Oestrus ovis) is sometimes called 

 nasal catarrh. The trouble resulting is caused by a worm 

 laid by a species of the gadfly within the nostrils of sheep 

 which crawls up into the remotest parts of the upper cav- 

 ities of the nostril adjacent to the brain, where it grows 

 to maturity, and in instances not a few leads to the death 

 of the sheep. This result usually follows from the in- 

 flammation produced, which extends more or less to ad- 

 jacent portions of the brain. The fly which lays the grub 

 was probably brought into America with the early im- 

 portations of sheep. It is widely distributed. It is more 

 troublesome in the mild than in cold latitudes, owing 

 doubtless to the longer period congenial to its develop- 

 ment. But as far north as the southern Canadian boun- 

 dary, in some instances, the losses from its presence are 

 quite serious. Because of the slow development of the 

 grub, it is much more harmful to old than to young 

 sheep. The fly which lays the eggs is of sluggish habits, 

 and seldom flies, save when in search of some place to 

 deposit its young. It then flies swiftly with a low whir- 

 ring sound. It is considerably larger than a house fly and 

 it is claimed that it has no mouth, its only instinct appar- 

 ently being to reproduce its kind. The young are de- 

 posited, not as an tgg, but as a maggot within the rim 

 of the nostrils of the sheep. The usual time of the ap- 

 pearance of the fly is probably June and July in the northern 

 states, but in the southern states it is doubtless present much 

 longer, as there the grubs may be found in the nasal cavi- 

 ties during all the year and in various stages of growth. 

 The sheep are much agitated when the fly makes its at- 

 tacks. In some instances as soon as a fly touches the nose 

 of a sheep it shakes its head and strikes the ground vio- 

 lently with the forefeet. Holding the nose close to the 

 ground, the sheep run away. In other instances they 

 crowd together during the heat of the day with the nose 



