18 Farmers’ Bulletin 1150. 
or is seen by them, often becoming frantic and holding the nose in 
the dust or against other sheep. The attack occurs usually during 
the heat of the day, the fly being quiet in the early morning and late 
afternoon. The grub migrates up the nostrils by means of its hooks 
and spines, and may make its way to the communicating cavities. 
Occasional grubs fail to leave the sinuses in time and become too 
large to get through the apertures they entered ; these die and usually 
become calcified. The grub in the sinuses feeds and grows until it is 
ready to leave the sheep. Sometime during the spring or summer, 
in temperate climates, the grubs leave the sheep and fall to the 
ground, into which they burrow a short distance. Their skin _be- 
comes hard and leathery and they lie quiescent for three weeks to 
two months, according to conditions of temperature and moisture. 
Finally the adult flies break out from the leathery envelopes within 
which they haye undergone their transformation from the preceding 
stage, like a butterfly in a chrysalis, crawl to the surface, and are 
ready to mate and then to deposit the young. 
Distribution—This parasite appears to be prevalent throughout 
the United States wherever sheep are kept. It is a common and 
troublesome pest, especially in the South. 
Symptoms and lesions.—<As the grub crawls about in the nostrils 
the hooks and spines set up an irritation which is at first acute with 
a resultant flow of serum from the nose, resembling a “cold in the 
head.” Presently the nostrils show evidence of bacterial infection, 
the flow thickens and becomes discolored, presenting the picture 
called by the sheepmen “ snotty nose,” a pronounced catarrhal condi- 
tion. The hooks and spines set up minute hemorrhages, which are 
visible on post-mortem examination as rows of blackened dots on the 
mucous lining of the nostrils and sinuses. One result of this irrita- 
tion and inflammation is a thickening of the mucous membrane, a 
condition which interferes with its normal function of smell and 
helps to close the breathing passages, which are already functioning 
improperly as a result of the thick, catarrhal secretions. As a con- 
sequence the sheep experiences difficulty in breathing, which tends to 
impair its general physical condition. Add to this the fact that the 
sinuses may become filled with purulent matter and that the toxins 
from the purulent matter here and elsewhere are constantly absorbed 
and there is evidently present a condition which must weaken an 
animal. Furthermore, the irritation due to the wandering of these 
spiny grubs over the sensitive mucous membrane of the nostrils 
prevents the sheep fronxresting or devoting its full time and energy 
to feeding and growing. 
Though the characteristic symptom of grub in the head is the 
profuse discharge from the nose, the sheep show other evidences of 
