35S 
OESTRUS. 
The principal European species is the Oestrus 
Bovis or Ox Gad-Fly. This is about the size of a 
common Bee, and is of a pale yellowish brown 
colour, with the thorax marked by four longitudi- 
nal dusky streaks, and the abdomen by a black 
bar across the middle, the tip being covered with 
tawny or orange-coloured hairs: the wings are 
pale brown, and unspotted. 
The female of this species, when ready to de- 
posit her eggs, fastens on the back of a heifer or 
cow, and piercing the skin with the tube situated 
at the tip of the abdomen, deposits an egg in the 
puncture: she then proceeds to another spot at 
some distance from the former, repeating the 
same operation at intervals on many parts of the 
animal’s back. . This operation is not performed 
without severe pain to the animal on which it is 
practised; and it is for this reason that cattle are 
observed to be seized with such violent horror 
when apprehensive of the approaches of the female 
Oestrus; flying with uncontrollable rapiditjg and 
endeavouring to escape their tormentor by taking 
Refuge in the nearest pond; it being observed that 
this insect rarely attacks cattle when standing in 
water. 
In the punctures of the skin thus formed b}^ the 
Gad-fly the several eggs hatcli, and the larva? by 
their motion and suction cause so many small 
swellings or abscesses beneath the skin, which 
growing graduall}^ larger, become externally visi- 
ble, exhibiting so many tubercles an inch or more 
