GAD-FLY. 
46l 
The different species of this genus make their 
attack on different animals, and each proceeds to 
deposit its ova in some particular part of the beast : 
while one pierces the hide, another lays its egg in 
the hair, and a third introduces them into the 
nostrils of the terrified animal. This last, or CEstrus 
ovis, is the torment of the sheep ; for, the moment 
it approaches, the whole flock become extremely 
agitated, shaking their heads, and striking their 
fore-feet violently against the ground. Conscious 
of the dreadful consequences of an attack, they en- 
deavour to avoid their enemy by holding their 
noses close to the earth, and running in every 
direction about the common. As they go along, 
they smell to the grass lest one of their tormentors 
should be lying in wait for them, and as soon as 
possible remove to the dusty road, or a neighbour- 
ing gravel-pit, where they crowd together with 
their noses so close to the ground that the fly is un- 
able to get at them. If the sheep are driven from 
this, they retreat to the grass: in the heat of the day 
the fly will be frequently seen to attack them, and 
the whole flock will be thrown into confusion. 
These poor animals have sufficient reason for their 
fears ; since the larvae hatched within their nostrils 
produce a degree of inflammation, and consequently 
pain, that only ceases when the hots fall to the 
ground preparatory to their passage into the state of 
a chrysalis. 
The other species of this genus contain nothing 
particularly deserving of notice, unless, according to 
