THE HOUSE FLY 79 



although infant paralysis can be spread by direct contact 

 between an infected child and a healthy one. 



This Biting Stable Fly is thought to have originated in 

 Europe, but it is now found in practically all parts of the 

 civilised world, spread, like the Brown, the Black Rat, and 

 the common House Fly, by the ships of trading nations. 



This species of fly cannot be readily distinguished from 

 the House Fly by the careless observer ; but when closely 

 examined it will be seen to differ in some noticeable ways. 

 The proboscis is quite differently constructed to that of 

 the House Fly. In the Biting Stable Fly the proboscis 

 contains a lancet with which it pierces the skin of its 

 host in order to feed upon the blood. On the contrary, 

 the House Fly's proboscis is only adapted for sucking up 

 liquid, or semi-liquid substances, and it is therefore in- 

 capable of piercing the skin of man or lower animals, owing 

 to the absence of a lancet. It differs from the House Fly 

 also in being more distinctly spotted with grey and black ; 

 and by the flagellum of the antennae being hairy on one 

 side only. An examination of the wings of the two species 

 of flies will also reveal a difference. The third long wing 

 vein in the House Fly will be seen to have a sharp elbow 

 near the tip, as shown in the illustration ; whereas in the 

 Biting Stable Fly this wing vein is bent to a much lesser 

 degree at the same place. 



The Biting Stable Fly feeds entirely upon the blood of 

 the mammal class of animals, including man. Its favourite 

 victims are horses and cattle, and in consequence it haunts 

 the stables and cattle kraals. Sometimes these flies are 

 so numerous that the horses and cattle are driven almost 

 frantic by their painful bites. 



