122 The Common House Fly. [Sess. 



badly-kept or dirty houses the fly plague is much iu evi- 

 dence. This is especially marked if remnants of food are 

 exposed. Warm, sunny, ill-ventilated, and dirty rooms are 

 the chosen habitat of the domestic fly. It rests during the 

 night, and only resumes its activity on the rising of the sun. 

 The brighter the sun and the warmer the air the greater the 

 activity of the fly. On the other hand, on cold sunless days 

 the fly becomes sluggish, until on the advent of cold weather 

 the sleep becomes a stupor, and passes into hibernation in the 

 case of a few flies. During its hours of activity its whole 

 time seems to be spent in feeding, or attempting to extract 

 nourishment from even what we might term arid wastes. It 

 is a voracious feeder, and it has been found that in a single 

 meal it frequently swallows nearly half of its own weight of 

 food. As its digestive system is very simple, it absorbs only 

 those substances which are readily soluble in its digestive 

 fluids, and evacuates the remainder, and this accounts for the 

 enormous number of fly specks on windows, furniture, or 

 metal goods. 



It is thought that the life of a midsummer fly does not 

 extend beyond three weeks, but in the autumn pet flies have 

 been kept several weeks. As with human beings, few die 

 from old age ; but the enemies of the fly are innumerable, 

 though perhaps the great majority succumb to the fly fungus 

 disease (Empusa muscce). They may be seen in great num- 

 bers, attached to ceilings, &c, dead, and on examination the 

 abdomen is found swollen by reason of an immense growth of 

 spore-bearing hyphse. These have invaded the body-cavity, 

 and all its internal organs are destroyed. Another cause of 

 death in regions where plague is common is the B. pestis. 

 Our poor fly, however, has its enemies upon it even during 

 life ; numerous parasites, in the shape of red-coloured mites, 

 make its life miserable. They cling tenaciously to the base 

 of the wings or to the abdomen. The cheese-mite is said to 

 pass its nymphal stage on the body of the house fly, and it 

 may be in this way that the delectable condition of our house- 

 hold viand arises. Several other varieties of parasite find a 

 host in the common fly — e.g., flagellate worms, nematodes. 

 Spiders also exact an enormous toll of fly life. 



A relatively small number pass the winter hibernating, 



