5 
SHEEP. 
Sheep’s Nostril Fly. (Estrus ovis , Linn. 
(Estrus ovis. —Fly, magnified, line showing natural length; maggot; 
mouth hooks of maggot; and tail segment, showing spiracles, and lobes, acting 
as organs of progression ; all magnified. After Brauer. 
The Sheep's Nostril Fly is from about two-fifths to half an inch 
in length, and slightly hairy. The upper part of the head and body 
between the wings of some shade of grey or dull yellow, spotted or 
mottled with dark markings. The abdomen yellowish, or white, 
mottled with dark brown or black; the under side similarly coloured, 
but “ with a dark spot in the middle of each ring.” Legs brown 
or yellowish brown; wings transparent, and when at rest extend 
beyond the body. Mouth wanting. There is a good deal of 
difference in the exact shades of colour described by various 
writers; from such as I have myself examined I should say that 
the fly might be described as spotted, or mottled with ash-grey, 
and black between the wings, and the abdomen also spotted with 
black and yellowish white, with a silvery lustre when alive. 
The presence of the Nostril Fly amongst the flock may be known 
by the sheep holding their noses close to the ground, shaking their 
heads, and striking the ground violently with their fore feet. 
Sometimes gathering together with their heads in the centre and 
their noses down to the ground, or buried in dust or sand if there 
is any, and occasionally one sheep going off at a gallop as if to 
escape from an enemy. 
The fly lays the eggs, or maggots lately hatched, at the opening of 
the sheep’s nostrils. Formerly it was supposed that the egg was 
laid, and hatched after being deposited, but many observations, 
ranging back to at least the middle of the last century, and given 
both by European and U.S.A. writers, record, beyond doubt, the 
fact of deposit taking place in the form of living maggots. Amongst 
special entomological observers, the late Prof. Eiley (Entomologist 
to the Department of Agriculture, U.S.A.) has recorded obtaining 
