THE INSECT WORLD. 



blood poisoning may be set up by a fly which has been feeding 

 upon a putrefying carcass and then feeds upon an abraded sur- 

 face or a cut or bruise on man. This, however, is not a common 

 occurrence, and perhaps as a scavenger the insect is about as 

 useful as it is annoying. A single female produces on an average 

 about one hundred and fifty eggs, and this, with the short period 

 required to bring them to maturity, accounts for the enormous 

 increase of the insects. After a fly has attained this stage it 

 never grows more, and a small fly never makes a large fly, any 

 more than the progeny of a large fly is ever a small fly. 



The "blow-fly," Calliphora vornitoria, is the largest of the 

 common species abundant enough to attract attention, and this 

 has the body of a deep blue, almost black, color, the abdomen a 

 little lighter and somewhat more shining. It is an obtrusive 

 creature and noisy withal, especially when flying about on the 

 windows or bumping against the ceilings of a room, making its 

 presence obnoxious in more ways than one. Its eggs are laid on 

 all sorts of animal and vegetable matter in an incipient stage of 

 decay. Meat exposed in summer is almost certain to show, in a 

 very short time, little piles of elongate white eggs scattered over 

 the surface here and there. Fish are especially subject to attack, 

 and I have myself had the experience that a little string of fish 

 laid in the shade of a bush on the bank was covered with such 

 eggs before I was ready to go home. Of course they could be 

 readily washed off, and it is not usual for this insect to retain the 

 eggs until they hatch within the abdomen, yet I have found 

 specimens that have done so. This species also requires but a 

 very short period for its development, and its rate of increase is 

 so great that it has given rise to the saying that a pair of flies 

 will devour an ox more rapidly than will a lion. A carcass left in 

 the fields during midsummer becomes, in fact, in a few days a 

 mass of maggots, which soon leave nothing but hide and bones. 

 A somewhat smaller species than this blow-fly, of a very much 

 - brighter green or bluish color, with four longitudinal lines on the 

 thorax, is the "screw-worm" fly, Lucilia 7nacellaria. This is a 

 common species throughout a large portion of our country, and 

 ordinarily feeds upon dead or decaying animal matter. Under 

 some circumstances, however, it attacks living animals, and in 

 the Southern and Southwestern States occasionally becomes a 



