222 SHEEP GAD-FLY. 



The young grubs, as soon as they are deposited in the 

 nostrils of the sheep, begin their migrations upwards into 

 the dark passages of the nose and frontal sinuses. This 

 movement is performed by means of hooks and spines, as the 

 maggots do not possess any legs. Of course the use of such 

 hooks and spines is very irritating to the sheep, and the 

 poor victims make man^'- attempts to get rid of their foes. 



The grubs remain about ten months in the nasal cavities 

 of the sheep. During this period they undergo a number of 

 molts; in the first stage they are white and almost trans- 

 parent, and measure about 2mm. in length; in the second 

 stage they are 6mm. in length, yellowish-white, and have 

 no spines except a few near the motith. In the third stage 

 the full size and form is attained as shown in fig. 180, 1>. 

 When mature the larvte detach themselves from the mucous 

 membrane, creep about, reach the nose, and are expelled by 

 the violent snorting of their host. A day later the larval 

 skin, which was thus far soft and of a reddish color, becomes 

 contracted, and gradually turns brown and black, forming 

 a puparium inside of ^vhich the future fl}^ is formed. This 

 pupal stage lasts from four to six weeks. If manylarvje are 

 present they cause in the sheep a catarrhal discharge on the 

 affected side of the nose; this is commonly known as "Snot 

 Nose." Neumann gives an excellent description of the symp- 

 toms: "Three or four larvje of the Oestrus are frequently found 

 in the frontal sinuses of sheep which, during life, have never 

 manifested any symptoms. It is only when the larvae are 

 numerous, and ^^hen they are quite well advanced in their 

 development at the commencement of spring-time, that they 

 occasion morbid troubles. The latter begin bA- a discharge, 

 often unilateral, which is at first clear and serous, then 

 thick and mucous. Frequently there is sneezing and snort- 

 ing, accompanied by the expulsion of mucus and sometimes 

 of CEsfrus larvfe. Later the animals turn the head backward, 

 often shake it, rub the nose against the ground or some 

 other object within reach, or with their front feet. As the 

 malady gradually advances the sheep go with lowered head, 

 lifting the feet high as if they were walking in water. Some- 

 times they quickly raise the head, carrying the nose to the 



