SHEEP GAD-FLY. 221 
weather, from May to October; in cold and rainy days it 
hides near the sheep-folds and in other protected places. 
Like all flies of this order it delights to rest on warm and ex- 
posed rocks found in high elevations. The gravid female, 
approaching flocks of sheep, scares and disturbs them very 
greatly, and they try all sorts of ways to prevent it from de- 
positing its young larve or maggots. . The sheep lie down, 
bury their noses in the dust, huddle together, and even raise 
clouds of dust to deceive their enemy. But generally all 
their efforts prove of no avail. Just one hundred years ago 
Mr. Clark so well described the effects of an attack of the fly, 

Fig. 181.—Sheep gad-fly from Cambridge Museum. Enlarged. Original. 
that his words arerepeated: ‘“‘the moment the fly touches this 
part (the nose) of the sheep, they shake their heads and 
strike the ground violently with their fore-feet; at the same 
time holding their noses close to the earth, they run away, 
looking about them on every side to see if the fly pursues. 
They also ‘‘smell to the grass,’”’ as they go, lest one should 
be lying in wait for them. Ifthey observe one, they gallop 
back, or take some other direction. As they can not, like 
the horses, take refuge in the water, they have recourse to a 
rut, or dry, dusty road, or gravel-pit, where they crowd to- 
gether during the heat of the day, with their noses held close 
to the ground, which renders it difficult for the fly conven- 
iently to get at the nostrils.”” As the gad-fly is only active 
during the warmer parts of the day the sheep can enjoy feed- 
ing early in the morning and late in the evening. 
