DISEASES OF SHEEP 525 



The sheep gad fly is unknown to the sheep breeder in any- 

 thing except the larval or grub state. The mature fly is like an 

 over-grown house fly of a dullish yellow color so closely covered 

 with small, black spots as to give the whole a brownish appearance. 

 The abdomen consists of five rings, velvety and variegated with 

 brown and straw color. The feet are brown; the wings are trans- 

 parent and quite large. The head is whitish underneath. There 

 are no mouth parts and the eyes are purplish brown. There are three 

 eyelets on the top of the head. The space between the eyes in the 

 male is very narrow, being less than one-third that of the female. 

 The fly is only obtained by hatching the grub in a cage and watch- 

 ing developments. They are very sluggish and remain in hiding 

 until fully matured and the temperature is sufficiently high. The 

 female rises high and flies swiftly to a flock and deposits an egg 

 containing a developing larvae. The male never bothers a flock. 

 The female only flies during the hot months and in the middle of 

 the day. 



The attack of a flock of sheep by these flies is attended with 

 the same fright as is seen when the horse gad fly strikes the horse's 

 nose. The sheep will push their noses down into the ground be- 

 tween their legs, run, stamp, snort and huddle together, seek the 

 shade of low sheds, or under buildings. The attack seems to strike 

 terror to them. The sheep are not molested during the morning or 

 evening. As the mature fly has no mouth parts or means of feed- 

 ing, it is evident that its sole mission is to propagate the species. 



The young bot begins to make its way up the nasal passage as 

 soon as it is deposited. This is accomplished by means of the hooks 

 and spines. The operation is attended with some tickling or irri- 

 tation as there is often violent sneezing and snorting but apparently 

 without avail. 



The larvae find their way to the superior part of the nasal cavity, 

 between the turbinate bones, the frontal or facial sinuses, or between 

 the ethmoid cells. Their presence causes some irritation and stimu- 

 lation of secretion, which they use as food. They live in this loca- 

 tion for several months, at least over the winter, and make their 

 escape in the spring. Ordinarily we do not find more than one, two, 

 or three grubs in the head of affected sheep. Occasionally eight or 

 ten will be seen. Some writers record from twelve to twenty grubs 

 in bad cases and there are records of from sixty to eighty. When 

 the number is small there are no serious symptoms. When there 

 are several, there is usually marked catarrhal discharge and we have 

 the thick effusive mucous characteristic of the snotty nose. 



Treatment. This must be preventive as far as possible. The 

 fly does not attack sheep in the shade and only seeks its prey during 

 the middle of the day. A low temporary shed that will afford shade 

 in the pasture will be a great protection. Valuable breeding stock 

 can well be stabled and allowed to graze during the morning and 

 evening. Some resort to putting tar on the noses every few days to 

 prevent attack. This can be done by smearing the sides of a narrow 



