THE SHEEP GADFLY-GRUB IN THE HEAD-NASAL 

 CATARRH. 



(EsTRUS ovis, Linn. 

 Plates I, II, and III. 



The popular names of this well-known parasite of sheep convey to 

 the reader its epitomized life history, long known to veterinarians 

 and farmers. Though the life history is a comparatively simple one, 

 there are many of its details which are not only unfamiliar to the aver- 

 age shepherd, but some of which are unknown even to those who have 

 made a special studj^ of these pests. 



The " Sheep Gadfly," the parent of the " Grub in the Head," is, 

 when flying, so small and so quick in its actions that it is very difficult 

 to see, and still more difficult to catch. The greater proportion of 

 specimens in collections have been raised from the grubs, i. e., the adult 

 grubs are collected and placed in a net-covered box, the bottom of which 

 is covered by a couple of inches of damp sand. In a few minutes they 

 bury themselves in the sand, and in from three to four weeks they re- 

 appear as flies. 



C. Y. Eiley {Insects Missouri^ First Annual Eeport, 1868, p. 161) de- 

 scribes the fly (Plate I, Fig. 11) as follows: 



lu this stage it looks something like an overgrown house-fly. The ground color of 

 the ujiper part of the head and thorax is dull yellow, but they are so covered with 

 little round, elevated black spots and atoms (scarcely distinguishable without the 

 aid of a magnifier) that they have a brown appearance. The abdomen consists of 

 five rings, is velvety and variegated with dark brown and straw color. On the 

 under side it is of the same color, but not variegated in the same way, there being a 

 dark spot in the middle of each ring. The feet are brown. The under side of the 

 head is puiied out and white. The antenuie are extremely small and spring from two 

 pbes which are sunk into a cavity at the anterior and under part of the head. The 

 eyes are pur]3lish brown, and three small eyelets are distinctly visible on the top of 

 the head. It has no mouth, and can not therefore take any nourishment. The wings 

 are transparent and extend beyond the body, and the winglets, which are quite largo 

 and white, entirely cover the poisers. Its only instinct seems to be the continuation 

 of its kind. It is quite lazy, and except when attempting to deposit its young its 

 wings are seldom used. 



The male is about as large as the female, but may be known by its 

 relatively narrower forehead or space between the eyes. Catching a 

 male at large would be a chance operation, for though they fly to mate 

 with the females around the sheep-yards and pastures, they never make 

 their presence known by disturbing sheep. 



25 



