130 INSECTS AFFECTING DOMESTIC ANIMALS. 
udder of cows. They often occur in the vulve of fresh cows, especially if there has 
been a retention of the placenta or afterbirth. Young calves are almost invariably 
affected in the navel, and often in the mouth, causing the teeth to fall out. One 
case occurred in the first stomach (paunch or rumen) that is worthy of mention. 
Last September the writer had occasion to kill a Jersey bull calf probably two months _ 
old that had screw-worms in both hind legs just above the hock joint. On opening 
the abdomen I found hair balls in the stomach (rumen), and, to my surprise, about 
twenty-five fully matured screw-worms almost buried in the wall of that organ. I 
placed some of the worms in moist earth, and in ten or twelve days they hatched 
out genuine screw-worm flies. How did they come there? My opinion is that the 
calf licked the sores on his legs, and in doing so took some eggs that hatched and 
developed in the stomach. 
Horses and mules are not so often attacked. In them they are usually found in 
barbed-wire injuries, and occasionally in the sheaths of horses and the vagine of 
mares and the navels of colts. 
Hogs are more liable to become affected than horses. They are frequently wounded 
by dogs and by fighting, or there may be barbed-wire injuries, wounds from castra- 
tion, etc. 
Sheep are comparatively free from the attacks unless injured by dogs. 
Weed considers that next to the attacks upon man those upon cattle 
are of most importance, and he estimates that half of the cases in cat- 
tle occur where ticks have been crushed. He also states that ‘‘sheep 
are attacked when injured by dogs, or when the sheep are in poor con- 
dition the eggs are laid upon the wool and when the larve hatch they 
immediately bore into the skin. In many cases the sheep are attacked 
within the nasal cavities and the worms eat into the head.” On hogs 
he says the favorite seat of attack is upon the ears. 
LIFE HISTORY. 
The fly which produces all this trouble is a small species less than 
half an inch in length (10 mm.) and of a bluish green color with metal- 
Fic. 63.—Compsomyia macellaria: adult, wings expanded—enlarged (after Francis). 
lic reflections. It is particularly distinguished from related forms by 
the presence of three longitudinal black stripes on the thorax. The 
head is reddish or yellow and the body is covered with stiff black hairs. 
