274 THE GAD-FLY AND ITS LARVA. 



Occasionally they stamp or strike violently with their fore- 

 feet near their noses as if an enemy, invisible to the spectator, 

 were assailing them at that point. It is the 

 CEstrus ovis, or gad-fly of the sheep, attempting 

 to deposite its eggs within their nostrils. "The 

 head and corslet" of this insect, says Mr. 

 Youatt, "taken together, are as long as the 

 body; and that is composed of five rings, tiger- 

 colored on the back, with some small points, and SHEEP G 

 larger patches of deep, brown color. The belly is of nearly 

 the same color, but has only one large circular spot on the 

 center of each of the rings. The length of the wings is 

 nearly equal to that of the body, which they almost entirely 

 cover. They are prettily striped and marked." * 



If the fly succeeds in depositing its eggs within the 

 nostrils of a sheep, they are immediately hatched by the 

 warmth and moisture, and the larvae or young grubs, crawl 

 up the nose finding their way to the sinuses, where, by means 

 of the tentacula or hooks which grow from the sides of their 

 mouths, they attach themselves to the membrane lining those 

 cavities, and there remain feeding on its mucus until the 

 following year. As the minute worm ascends the nose, the 

 sheep appears to be distracted with apprehension. It dashes 

 wildly about the field, stamping, snorting and tossing its head. 

 Fig. 1 in the annexed cut, exhibits the larva or grub about 

 half grown. It is then white, except two brown spots near 

 the tail. Fig. 2 represents it of full size. The rings, and 

 particularly those nearest the tail, are now dark brown. 



THE "GRUB" OR LARVA OF THE GAD-FLT. 



Each ring has darker spots, and below them are others, as 

 seen in Fig. 2. Fig. 3 exhibits a full grown larva on its back 

 the minute dots between the belly rings representing small 

 red spines, the points of which turn backwards. 



The larva, after remaining in the sinuses through the 



* Those who wish a further description of this insect, will find more on the 

 subject in Mr. Youatt' s work on sheep, and especially in Mr. Bracy Clark's mon- 

 ograph of the oeatrua ovis. 



