156 THE BLOW-FLY. 



Species of blow-, meat- or flesh-flies belong here. But some of 

 them are not satisfied with simply trying to obtain food for 

 themselves, but take care of their offspring by dropping 

 either eggs or larvae upon the host. Many species of blow- 

 flies have this habit, and as they produce living young and 

 as these increase rapidly in size, they can cause trouble, even 

 death. The viviparous females retain the eggs in spiral 

 dilations of their oviducts until hatched, when they are de- 

 posited upon decaying flesh of all kinds. The sexual organs 

 of the horse, cattle, and hogs, the interior of the ears, but 

 principally wounds and sores are selected by such flies and 

 here they drop living maggots in large numbers. Whoever 

 has observed even fairly fresh meat exposed for but a few- 

 moments in places where blow-flies abound must have seen 

 the innumerable small heaps of very minute maggots de- 

 posited upon it. The female flesh-fl^' {Sarcojjhaga carnaria 

 Linn.) can deposit at least 20,000 of these maggots, and as 

 they grow veryrapidh' they consume a large amount of food, 

 and forcing their way into the festering substance about 

 them they soon enlarge sores ("living sores"), and make them 

 very dangerous. All these flies multiply very rapidly, pro- 

 ducing many generations during the course of a ^v arm season. 

 It has been computed that a single female, within six months, 

 can have 508,000,000 descendants. No wonder, then, that 

 they can devour the carcass of a large animal in a few days, 

 and that we have so many flies about dwelling-places 

 and stables not kept clean. 



The maggots of these flies grow so rapidly, if food is 

 plent3^, that from a mere speck they grow in two or three 

 days to half an inch in length. They are whitish, long, soft- 

 bodied, footless, and are smaller towards the head and 

 thicker and blunt behind. When full-grown they leave their 

 odoriferous food and crawl to some convenient spot, force 

 their way into the soil, where they contract into elongated- 

 oval, barrel-shaped, and reddish-brown puparia, inside of 

 which the adult insects are formed. This requires but a very 

 short time, a few days, and the winged fly issues ready to 

 start another generation. Fig. 130, plate X, illustrates this 

 common insect. 



