WARBLE FLIES 
Cc. W. HOWARD. 
Until the spring of 1914, the pest of cattle, known as ox- 
warbles or warble-flies, seemed to have been absent from Minne- 
sota. But at that time, three cases of infested cattle which had 
been shipped in from other states, came to our attention. The 
injury to cattle is caused by the grub stage of the insect which 
lives in large tumors under the skin on the back of the cattle. 
When numerous, the loss due to the weakened condition of the 
cattle, as a result of the presence of these warbles is very con- 
siderable. At the Union stock yards, Chicago, it is estimated 
that during the grubby season, fully 5 per cent of the cattle re- 
ceived are grubby and the accompanying perforation of the hides 
by the grubs lessens their value on the market. When the flies 
are laying their eggs upon the hair of the cattle, the fretting and 
stampeding cause a loss in milk and beef. Osborn states that, 
considering the animals’ comfort as a mere matter of sentiment, 
it is fair to estimate that the average annual loss in the United 
States from this insect should be reckoned at $1.00 per head. Us- 
ing the census of 1910 as a basis, this would give us a loss of 
$69,000,000 annually. These flies are present in the greater part 
of the eastern and middle-western states and Canada. Apparently, 
Minnesota is an oasis in the center of an infested area. For this 
reason, great care must be exercised to prevent this pest being 
brought in from neighboring states and obtaining a foothold 
here. The three importations last spring to which we have 
referred, came from Massachusetts, New York and Wisconsin. 
The fly which produces these warbles is one of the bot-flies 
and resembles slightly a large, dark-colored bee in general appear- 
ance. They appear early in spring and last well on into summer, 
from March until July being the months of appearance. The eggs 
are placed on the hairs of the legs, preferably in the region of the 
hock and back of the knee. The fly is not provided with a sting 
and its mouth-parts are rudimentary, so it is unable to do any 
injury to the cattle, but when depositing an egg, strikes the 
