VERMINOUS BRONCHITIS, NASAL GRUB, CATARRH 155 



appears in the middle of the day, from July to September. 

 Sheep become excited when the tiy is around, and hold their 

 noses to the ground or against each other, although the fly does 

 not bite or sting. The young larva^ are deposited about the nos- 

 trils of the sheep from whence they crawl up into the various 

 cavities of the head, including the horn cores, and may even 

 reach the brain substance. They mature in about nine or ten 

 months and escape from the nose during the spring and early 

 summer. They then pass through another stage before the adult 



Fig. 52. — Sheep Gadfly (CEstrus ovis). 

 Commonly called "nasal grub." a, adult; b, larva; c. puparium. 



fly appears, which occurs in four to seven weeks from the time 

 the grubs escape from the nose. 



Symptoms. — A few larvje may not cause any evident disturb- 

 ance. When present in larger numbers, the parasites cause 

 great irritation accompanied by a marked catarrhal discharge 

 from the nostrils. The affected animals may refuse to eat well 

 and even cough. The sheep sneeze, shake their heads, and rub 

 their noses and faces against their feet or other objects; some- 

 times there are attacks of vertigo, and the walk may be unsteady 

 or irregular ; severe eases may develop con\'ulsions and die. The 

 nasal mucous membrane becomes thickened and this, with the 

 discharge, interferes with respiration. Such sheep are unthrifty 

 on account of the constant annoyance. On examination post 

 mortem, grubs are found in the various openings and chambers 



