180 FLIES. 



Oestrus. — Gad Fly, 



The Ox Gad-fly, is about the size of a 

 common bee, and is of a pale yellowish 

 brown colour, with the thorax marked by four 

 longitudinal 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 un- 

 spotted. 



The female of this insect, when ready to 

 deposit her eggs, fastens on the back of a 

 heifer or cow, and piercing the skin with the 

 tube situated at the top of the abdomen, 

 deposits an egg in the puncture ; she then 

 proceeds to another spot at some distance 

 from the former, repeating the same opera- 

 tion at intervals on many parts of the ani- 

 mars back. This operation is not performed 

 without severe pain to the animal on which 

 it is practised ; and it is for this reason that 

 c^le are observed to be seized with such 

 violent horror when apprehensive of the ap- 



