ORDER VII. TWO-WINGED INSECTS, OR FLIES. 303 



against the attacks of all insects, these flies will scent it a 

 great distance, and, arriving at it in crowds, they deposit 

 upon it their eggs, which are commonly called fly-blows. 



The maggots of this fly are well known in meat-shops, 

 pantries, and kitchens, and are every where considered as 

 disgusting in the extreme. They are spindle-formed, white, 

 soft, and armed with two horny hooks, which enable them 

 to move, and tear small pieces from the meat for their food. 

 It is surprising how fast these maggots will develop. 

 Signor Redi, a distinguished Italian naturalist, placed a 

 fish at the disposal of these flies, upon which they soon de- 

 posited their eggs. The second day after these maggots 

 were hatched they doubled in size, when thirty of them 

 weighed one grain ; but from that moment they grew so 

 fast, that on the next, or third day, one maggot alone 

 weighed seven grains, thus becoming two hundred times 

 heavier in twenty-four hours. These maggots arrive at 

 their full growth in about four days, when they creep to 

 the ground, change into an egg-shaped pupa, and come out 

 as perfect flies a few days after. 



A great deal of instinct is exhibited by these flies in re- 

 gard to the locality where they deposit their eggs, which 

 must be a place that will furnish good food for their off- 

 spring : for instance, if you set before them a thin piece of 

 meat, however good, they will move over it and feed upon 

 it, but will not deposit an egg upon it, because they know 

 it will soon dry up ; but if you put a piece of meat upon a 

 damp or moist ground, where it will decay rapidly, it will 

 soon be covered with eggs, the maggots of which will 

 scratch it with their hooks, and soil it with their fluid 

 evacuations, causing the whole piece to putrefy very rapidly 

 and become fetid. 



The Meat-fly is a great lover of human cadavers, and 

 in ancient times the people were much excited when it was 

 ascertained that a human corpse was actually devoured by 



