THE EOT- OR WARBLE-FLY 39 



It seems odd that an insect pest, which 

 so seriously affects our supply of leather, of 

 meat, and of milk, should have been studied 

 for over a century and yet conceal its chief 

 secret from man. But the problem is much 

 more difficult than the layman thinks. 



Whatever be the route the maggot travels 

 through the body of the calf or cow, by the 

 spring the fourth larval stage — when it is about 

 an inch long, and perhaps half as much in 

 breadth — is reached in the ' warble ' or cyst, 

 under the skin. Here, nourished by the 

 products of the inflammation it sets up, and 

 breathing by two spiracles at the hinder end 

 of its body, which are directed to the opening 

 of the ' warble ' which it has pierced through 

 the skin, the larva rests until one fine morning 

 it pushes its way, aided by its stout bristles, 

 through the opening and tumbles into the 

 outer world. 



Apparently it does not think much of its 

 new surroun(^ngs, for it loses no time in hiding 

 under some clod of earth or stone or crevice 

 in the soil, and straightway turns into a dark 

 brown pupa or chrysalis. This stage lasts three 

 to four weeks, and then the perfect fly emerges, 

 and will soon be ready to lay her eggs on some 

 new victim. 



As a rule it is the yearlings who suffer 

 most, and then the two-year-olds; the older 



