102 INSECTS AFFECTING DOMESTIC ANIMALS. 
THE SHEEP BOT-FLY OR HEAD MaceorT.! 
(@strus ovis Linn.) 
This insect, like the other members of the family, has been known for 
centuries, and has been equally dreaded by the animals it infests. It 
was mentioned by the Greek physician, Alexander Trallian, as far back 
as the year 560. Notwithstanding that it has been so well known, very 
different estimates have been placed upon the injury it may cause. 
Indeed, some writers have gone so far as to claim that no injury results 
from its presence, and to ridicule the idea that sheep die of “ grub in 
the head.” Even so high an authority as Mr. Youatt declares: 
It is incompatible with the wisdom and goodness that are everywhere evident, in 
proportion as the phenomena of nature are closely examined, that the destined resi- 
dence of the @strus ovis should be productive of continued inconvenience or disease. 
Mr. Randall is correct in saying that “ this is as farfetched as a con- 
clusion as the reasoning on which it is founded.” If the grub in the 
head is not productive of inconvenience or disease, whence the suffer- 
ing condition, the loss of appetite, the slow, weak gait, the frequent 
coughing, the purulent matter, sometimes so profusely secreted as at 
times to almost prevent the animals breathing? Whence the tossing 
and lowering of the head, and the fits of frenzy to which so naturally 
quiet and gentle an animal as the sheep is subject? All these symptoms 
result from grub in the head, and the animal frequently gets too weak 
to rise, and finally dies. These effects of the grub were well recognized 
and understood by such old writers and close observers as Réaumur 
and Kollar, while numerous flock masters of close observation who have 
suffered from this pest agree in ascribing these symptoms to this cause. 
It would be as reasonable to believe that those parasites are beneficial 
which are so injurious to man either internally or externally, or those 
which prey upon our caterpillars and other insects, and invariably 
destroy them. For although when there are but few grubs in the head 
the injury may not be perceptible, they can never be beneficial, and 
when numerous will undoubtedly cause death. They can notlive in the 
head of the sheep without causing great irritation by the spines with 
which the ventral region is covered and the hooks with which they cling to 
such a sensitive membrane as that which lines the sinuses. Moreover, 
when numerous enough to absorb more mucus than the sheep secretes the 
grubs will feed on the membrane itself, and (according to the evidence of 
some practical sheepmen) will even enter the brain through the natural 
perforations of the ethmoid bone, through which pass the olfactory 
nerves, in either of which cases they must cause the most excruciating 
pain. The natural fear also which the sheep have of the fly and the 
pains they take to preventits access to the nose are of themselves proof 
that itis obnoxious to them. The pest appears to have been more abun- 
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1 Adapted in part from Riley’s Mo. Rep. I, pp. 161-165. 
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