INSECTS AFFECTING DOMESTIC ANIMALS. 



The Screw Worm. 



Compsomyia macellar ia. 



The Screw Worm, so far as its injuries are con- 

 cerned, is a southern insect. Until recently little or 

 no damage from it had been reported outside of 

 Texas, but lately it has been injurious in Louisiana, 

 Mississippi, and other Southern States. The fly, 

 however, occurs throughout America ' from Canada 

 to Patagonia,' probably breeding in northern latitudes 

 in decaying animal and vegetable matter. Although 

 in the South cattle are specially liable to the attacks 

 of this insect, it is by no means confined to them, 

 for horses, mules, hogs, sheep, dogs, and in some re- 

 corded cases even men, suffer on account of it. 



" In all animals alike," according to Dr. M. Francis, 

 who has studied this insect carefully, " the eggs, after 

 being laid by the fly, hatch into larvee or so-called 

 ' worms.' The exact length of time this requires 

 seems to vary with circumstances. My present 

 opinion is that if the eggs are laid in a moist place 

 and on a warm day, it requires less than one hour ; 

 whereas, if laid in a dry place they seem to dry up 

 and lose their vitality. The young larva 1 , when first 

 hatched, are small and easily overlooked. If they 

 are hatched on the surface in a drop of blood from 

 a ruptured tick, for instance, they attempt to perfor- 

 ate the skin, and if hatched in wounds they at once 



